Square cube law would say so. The more surface area per volume to dissipate heat the better.

The inverse can be seen in arctic animals that are basically baubles to conserve heat.

Based on my experience gaining and losing weight and the amount I sweat when I'm heavier, I'd guess yes.

Not a genetic adaptation like OP is considering, but if you're a big westerner and spend a lot of time in a tropical country you're likely to lose weight.

Edit: tried to find some peer reviewed evidence to back up my anecdote but came away empty handed. Still i stand by my claim. :)