Body weight would make sense, but notice in both my examples I used the same toons (Juan and Rick). In both examples Juan took the direct hit, but only slid in one of the examples.
This is a bug, as I noticed that it isn’t even consistent between the spawn points - try this on Favela for example. If you start first, you can slide both toons in your spawn, but if you start second, and replicate the EXACT same positioning, only one toon moves
(As if going second needed ANOTHER disadvantage on that map)
I don’t have screenshots (I’m done with playing favela, it sucks if you go second, and quickly got sick of it), but this issue is easy to replicate there.