Another soundstage question

There are a couple of soundstage related threads running on the amp/preamp section and they reminded me of a question I’ve been meaning to ask without hijacking those threads. The speakers are Vandersteen 2Ci and the system along with their placement is giving me a real deep and relatively wide soundstage - but not much further to the sides, but I’d like the height of the soundstage be little higher. The speakers are on the sides of a bay window, about 10’ apart and with heavy drapes pulled on either side and about 2.5’ behind the speakers. Much lighter curtains cover the bay windows for privacy. In my seating position that is about 10’ away from each speaker the top of the soundstage is just about the top of the speakers, sort of like I’m sitting at the same level as the musicians. The depth is realistic but I think the height needs to higher to give a better feel for the height of the singer standing in the middle and the rest of the band scattered at different levels within the stage. So having said all this, is the soundstage height mostly a function of the electronics driving the speakers or its the size/shape of the speakers, e.g., speaker height, tilt, etc., the listening placement, or a combination of all of the above. Thanks.