<Space_Tactical_Unit_Cap>288</Space_Tactical_Unit_Cap>
That's the line, directly out of my Factions XML. That one is for the rebels (although I did set all factions to 288). Not sure why it isn't working for you...You do make sure to save it, right? Can't think of anything else that would cause this.
Oh I found out what it was, You have to save and then CLOSE the XML before launching the mod. Otherwise it gives you a population limit of 20 in space skirmishes.