Reledmac - interline (line spacing)

A simple question. Is there any way to change the interline of a Reledmac text (namely, between a \pstart and a \pend) without messing the algorithm of page-breaking?

I tried to move up the 11.5 from my \fontsize{10}{11.5}\selectfont

but it ends up in a total mess, even with a small shift.

The \renewcommand\baselinestretch{2} has no effect, too.

Reading the manual, maybe (perhaps!) that this behaviour has something to to with this:

\add@penalties is the last macro used by \do@line. It adds up the club, widow, and interline penalties, and puts a single penalty of the appropriate size back into the para- graph; these penalties get removed by the \vsplit operation. \displaywidowpenalty and \brokenpenalty are not restored, since we have no easy way to find out where we should insert them.

So, what could I do to get a bit of space between the lines without messing the mise-en-page?