These things are apparently fast. I don't have faith in our ability to kill something before it does anything.
Assuming I'm correct (which, granted,
if I'm right) I'd rather get a shot at it/a chance to stick this creature while it's just leapt out of the muck rather than when it's charging at us full-speed. It's an even less appealing option to fight these things when they are ready and aware of their surroundings.
And what if it doesn't come from the swamp? We know Tlalli started tracking her target on another level, so they clearly aren't tied to the swamp in any way that would force them to be there. What if it comes from a place closer to Sophie and out position is too far away to do anything with any accuracy?
Sure, that was a bit of curious speculation on my part. Was just wondering if this is their habitat - obviously, as treave said, that's not the case. These things aren't tied to the swamp and it's not their "habitat" for lack of a better word. But nonetheless, both of them came from the swamp, and it seems to be a great place to hide. While it's possible for them to come from elsewhere, they've all attacked us from the same area so far.
I think it helps to put ourselves in the shoes of the shapeshifter:
A crazy old-lady Hunter is coming after me? What do I do? I know she's going to track me down eventually, so I try and even the odds by making the battlefield conditions favourable. I allow her to track me down, then get her stuck in a bunch of mucky swamp water with poor visibility, where I also get a few of my allies to to lie in wait as well (after all, where else would they hide?). A swamp seems like a great place to turn a trap against your would-be pursuer.
They could be anywhere, I acknowledge that, but one has already emerged from the swamp that we haven't accounted for, and I reckon that there wouldn't be any other nearby areas where it would be as easy to hide.
Your logic (which makes perfect sense!) is this: Sophie is our eyes and ears on the battlefield > Sophie is vulnerable > Stay close to Sophie and attack anything coming her way. I'm just taking that one step further; my logic goes, Sophie is our eyes and ears on the battlefield > Sophie is vulnerable > Prevent any threats from reaching Sophie. And so far, since all of our threats have come from the swamp, I think that we ought to focus our efforts there.
Anyways, I think that'll be it for my posting on and on about this choice - think I've said my piece. I just felt particularly passionate about this one and wanted to open up the discussion a bit.