Yeah, lots of mixed comments on that. BigBattery sells thousands of these cell-type packs and no issue with side mount. Yes, Will had one that leaked.I remember reading that having those batteries on their side can be problematic. (I don’t remember which side is ok). That is something to read the spec sheet very carefully.
I do have room to mount vertically, it's just a much tighter fit. I'll have to consider my options.
EDIT: I've asked Amy for a definitive answer on mounting orientation of EVE cells from the factory. Let's see what THEY say.