I think you are burning off the extra calories you eat when you go for the longer ride. So, I don't think that is it. I think it's the two short rides are like interval work. Which, I had leveled off my weight and never thought I would see anything lower. When I added those short burst of intervals, it fell right off!

I assume you are probably really hussling it when you are commuting it to work. Trying to be on time to your employer etc. (not saying that moving at a snails pace by any means on the longer rides, btw, I'm sure). It's those short sustained bursts that just fry off that extra bit of fat.

I think the split in the time of day just re-kick-starts your metabolism again from the morning ride. It all plays together, IMHO.

Good for you on the jeans, btw.