How to position tikz node relative to 2 other nodes

Question

Suppose, I have this structure:

Code:

\documentclass{standalone}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage{tikz}
\usetikzlibrary{calc,shapes, positioning}
\begin{document}
\def\len{1cm}
\begin{tikzpicture}[node distance = \len, auto]
\tikzset{
    line/.style = {draw},
    block/.style = {rectangle, draw, text centered, minimum height=2em},
}
\node [block] (1-1) {1-1};
\node [block, below = of 1-1] (1-2) {1-2};
\path [line] (1-1) -- (1-2);
\node [block, below right = of 1-2] (2-1) {2-1};
\path [line] (1-2) -| (2-1);
\node [block, right = of 2-1] (3-1) {3-1};
\node [block, dotted] at(3-1|-1-2) (3-2) {3-1};
\path [line] (1-1) -| (3-1);
\end{tikzpicture}
\end{document}

How can I position node 3-1 to the right of node 2-1 and on the same level with 1-2, using calc library? I drew the desired position, using dotted borders.

Please, don't suggest to use matrix.

Update

1 approach is to use above right = of 2-1. It would work for this test case, but if node 1-2 is tall, it wouldn't position 1-3 vertically to the centre of it:

\documentclass{standalone}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage{tikz}
\usetikzlibrary{calc,shapes, positioning}
\begin{document}
\def\len{1cm}
\begin{tikzpicture}[node distance = \len, auto]
\tikzset{
    line/.style = {draw},
    block/.style = {rectangle, draw, text centered, minimum height=2em},
}
\node [block] (1-1) {1-1};
\node [block, below = of 1-1, text width = 1cm] (1-2) {text, text, text (!): $\frac{1}{2}$};
\path [line] (1-1) -- (1-2);
\node [block, below right = of 1-2] (2-1) {2-1};
\path [line] (1-2) -| (2-1);
\node [block, above right = of 2-1] (3-1) {3-1};
\path [line] (1-1) -| (3-1);
\end{tikzpicture}
\end{document}

Gives this:

Update 2

@Bordaigorl suggested to use right = 2 of 1-2. But if 2-1 is wide, it will visually overlap with 3-1:

\documentclass{standalone}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage{tikz}
\usetikzlibrary{calc,shapes, positioning}
\begin{document}
\def\len{1cm}
\begin{tikzpicture}[node distance = \len, auto]
\tikzset{
    line/.style = {draw},
    block/.style = {rectangle, draw, text centered, minimum height=2em},
}
\node [block] (1-1) {1-1};
\node [block, below = of 1-1, text width = 1cm] (1-2) {text, text, text (!): $\frac{1}{2}$};
\path [line] (1-1) -- (1-2);
\node [block, below right = of 1-2] (2-1) {2-2-2-2-2};
\path [line] (1-2) -| (2-1);
\node [block, right = 2 of 1-2] (3-1) {3-1};
\path [line] (1-1) -| (3-1);
\end{tikzpicture}
\end{document}

Possible solution

I used an extra \coordinate node to the right of 2-1. Is it possible to solve the problem without it?

\documentclass{standalone}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage{tikz}
\usetikzlibrary{calc,shapes, positioning}
\begin{document}
\def\len{1cm}
\begin{tikzpicture}[node distance = \len, auto]
\tikzset{
    line/.style = {draw},
    block/.style = {rectangle, draw, text centered, minimum height=2em},
}
\node [block] (1-1) {1-1};
\node [block, below = of 1-1, text width = 1cm] (1-2) {text, text, text (!): $\frac{1}{2}$};
\path [line] (1-1) -- (1-2);
\node [block, below right = of 1-2] (2-1) {2-2-2-2-2};
\path [line] (1-2) -| (2-1);
\node [coordinate, right = of 2-1.east] (3-1) {};
\node [block] at(3-1|-1-2) (3-2) {3-1};
\path [line] (1-1) -| (3-2);
\end{tikzpicture}
\end{document}

Answer 1

You may use right=of 2-1 |- 1-2 (without calc library):

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning}
\begin{document}
\def\len{1cm}
\begin{tikzpicture}[node distance = \len, auto]
\tikzset{
    block/.style = {rectangle, draw, text centered, minimum height=2em},
}
\node [block] (1-1) {1-1};
\node [block, below = of 1-1] (1-2) {1-2};
\node [block, below right = of 1-2] (2-1) {2-1};
\node [block,right=of 2-1 |- 1-2] (3-1) {3-1};
\end{tikzpicture}
\end{document}

Answer 2

You can use positioning for that by asking it to place 3-1 "two to the right" of 1-2:

\begin{tikzpicture}[node distance = \len, auto]
    \tikzset{
        line/.style = {draw},
        block/.style = {rectangle, draw, text centered, minimum height=2em},
    }
    \node [block] (1-1) {1-1};
    \node [block, below = of 1-1] (1-2) {1-2};
    \path [line] (1-1) -- (1-2);
    \node [block, below right = of 1-2] (2-1) {2-1};
    \path [line] (1-2) -| (2-1);
    \node [block, right =2 of 1-2] (3-1) {3-1};
    % \node [block, dotted] at(3-1|-1-2) (3-2) {3-1};
    \path [line] (1-1) -| (3-1);
\end{tikzpicture}

However this does not scale well if the nodes have dissimilar sizes.

To accommodate all the constraints one can use the on grid option that, when using positioning keys, instructs TikZ to use centers of nodes as reference points for positioning:

\begin{document}
\def\len{2cm}

    \begin{tikzpicture}[x=\len, y=\len, on grid]
        \tikzset{
            line/.style = {draw},
            block/.style = {rectangle, draw, text centered, minimum height=2em},
        }
        \node [block] (1-1) {1-1};
        \node [block, below =1 of 1-1, text width = 1cm] (1-2) {text, text, text (!): $\frac{1}{2}$};
        \path [line] (1-1) -- (1-2);
        \node [block, below right =1 of 1-2] (2-1) {2-2-2-2};
        \path [line] (1-2) -| (2-1);
        \node [block, right =1.5 of 1-2] (3-1) {3-1};
        \path [line] (1-1) -| (3-1);
    \end{tikzpicture}
\end{document}

A few changes are needed:

1. here the distances must be changes since now they stand for distances between centres, not borders (hence \def\len{2cm})
2. we use explicit dimensionless relative coordinates in the positioning keys to be able to scale if necessary using the x and y keys

Now you can add content to the nodes as you wish but they remain in their relative positions, as now they are relative to the centres. If later on the spacing is not enough you can redefine \len (or x and y individually) to space the nodes out.