I think your theory is correct and saabluster is wrong, but i dare not say so in open forum (I'm a learning newbie).
If you direct a beam of light on to a wall, lets say 30 lumens, then direct another beam of light of 20 lumens on to the same spot on the wall, the intensity of the hotspot increases. So this must increase throw.
So, what you say is correct regarding the much bigger sst90 emitter. The emitter surface might not be as bright as xr-e but it is a lot bigger and if this can be concentrated to a tight beam, all those photons tightly packed are going to outthrow the much smaller slightly brighter emitter. Does this make sence ?