Here.
settings / workspace / save current window size.
as long as the window size respects apples rules (stacking windows, making windows bigger than the screen…) it should stick.
in this message I explain 2-3 little things people tend to see as interface bugs in SU that are actually Apple enforcing its design rules. if you disobey these rules, the standard window will be a bit resized
depends on the parameter he choose, in my case, it minimises