Problems using lmodern with very small font sizes

Question

Due to page restriction from my university I had to optimize my formulary sheet by writing more compact. Therefore I switched from the default Computer Modern Roman font to Latin Modern but now I get a problem with Integrals, Sums, etc. For example the integral got pretty big which is for my taste pretty ugly. (Additionally I used lmodern because I wanted to get rid of the over proportional super- and subscripts when I use fontsize = 6pt)

Can somebody please explain to me why lmodern increases the size of integrals "by default" and give me a decent solution in solving this problem to get the old size back for integrals, sums, ...

\documentclass[a4paper, fontsize=6pt]{scrartcl}

\usepackage[T1]{fontenc}
\usepackage{lmodern}

\DeclareMathSizes{6}{6}{4}{4}

\begin{document}

    \begin{equation}
        W_{12} = \int\limits_\gamma \mathbf{F} \cdot d\mathbf{r} = T_2 - T_1
    \end{equation}

\end{document}

Furthermore I added two pictures, one with the default font and the other one with lmodern showing the problem exemplary.

Answer 1

It's a problem with lmodern defining the math extension font at a fixed size. See sum symbol in tikzposter too small for the opposite problem.

\documentclass[a4paper, fontsize=6pt]{scrartcl}

\usepackage[T1]{fontenc}
\usepackage{lmodern}

% declare `cmex` to be arbitrary scalable
\DeclareFontShape{OMX}{cmex}{m}{n}{
  <-7.5> cmex7
  <7.5-8.5> cmex8
  <8.5-9.5> cmex9
  <9.5-> cmex10
}{}
\SetSymbolFont{largesymbols}{normal}{OMX}{cmex}{m}{n}
\SetSymbolFont{largesymbols}{bold}  {OMX}{cmex}{m}{n}


\DeclareMathSizes{6}{6}{4}{4}

\begin{document}

    \begin{equation}
        W_{12} = \int\limits_\gamma \mathbf{F} \cdot d\mathbf{r} = T_2 - T_1
    \end{equation}

\end{document}