I don't know what eats that much RAM - when I'm loading the training_a map the UfoAI process eats 270 Mb RAM, when I put it to background all OpenGL textures are destroyed and it takes up 200 Mb RAM. So textures occupy only 70 Mb, everything else should be internal game structures, I wonder why it's that many.
I can try one lame-ass optimization - when loading map restart UfoAI process so it won't load any menu and earthscape data, only the battlescape, but I don't think it will change things dramatically.
There are some huge structures allocated for map BSP tree and for pathfinding, as far as I understood by reading sources halfyear ago.
Android 2.3 official device requirements document requires device to have at least 128 Mb userspace RAM (that is, not used by device drivers), Android 4.0 document requires 340 Mb userspace RAM - that's enough for most maps in UfoAI I guess.
Edit: training_a map launched from Skirmish menu, with multiplayer equipment takes 330 Mb RAM with sounds, and 280 Mb without them (I've removed sounds from 1base.pk3, add or remove few megabytes due to randomized item generation). lake_ice map did non load with sounds at all, but it loaded without them, and used 330 Mb RAM (but crashed after a while). And bunker map crashes even without sounds (I remember playing it halfyear ago though)
335 Mb is the limit of my HTC Evo, when it kills foreground app, it could be higher if the stock firmware wasn't preloaded with lot of crap, the home screen process is the biggest among them and takes up 70 Mb RAM. And the actual RAM accessible to user space is 425 Mb, as shown by "adb shell cat /proc/meminfo".