> I think with higher body fat my body could simply burn that fat for energy, whereas that surplus simply isn't there.

It’s anecdotal, but I believe I’ve experienced similar effects. During my teenage years and for most of my twenties, my body fat percentage was low because I chronically under-ate (mostly just due to bad habits, though there was a financial component too at one point) and was pretty thin. Energy peaked and valleyed quite a bit with the after-lunch crash being the worst.

After I started working out and adjusted eating habits to accommodate that, my baseline weight jumped 20lbs or so. Some of that was muscle, but body fat percentage increased too. Since then energy levels have been much more even throughout the day, even during periods where I wasn’t working out (e.g. during pandemic lockdown) and I think it’s because there’s always a bit of fat to burn where there hadn’t been before.