For larger minis (like the taller version of the Catapult I had in my above images), I like to use IWM's 32mm bases- most minis fit without any trouble on them, and while they don't fit exactly in the lines on a hex map it's close enough that you can still play the game without any major confusion unless things turn into a total close-combat furball. (Reaper's CAV bases are even better, but a bit difficult to find these days for me)