This parameter is related with your casing thickness... So it won't allow for a hang less then your casing thickness... Which seems logic for a sill. Do you really want the sill set back to the window frame?
In dealing with some existing conditions, actually, yes... and it's not so much that the sill is proud of the casing but that the sill is proud of the wall. Dealing with a couple of situations where the existing building has been re-sided and the new siding extends past the window (not ideal, I know, but it's what's there).
Changing that wall closure to custom helped get me close enough, it's not past but it's not sticking out as far.
Thanks for your help!
Bill Szustak RA
Principal, Springboard Design
ArchiCAD 23, Windows 10
Ok. Fair enough.
In alternative, you could create an empty opening and fill it with another transparent wall with a proper width. Then insert your window in this transparent wall. This way you'd have total control of your window width without changing the wall.