The case of the missing fuel after fill-up

I've seen a few queries about the apparently missing fuel after topping off the tank and then after riding a little bit it settles out and is too much to be accounted for by the short time the engine was running alone. So today as I was prepping my bike for a race tomorrow and filling up, I topped it off and thought I'd pull the seat to see where the air pocket was.

Tank full, brimming just under the cap, fill line marked in red:




Under the seat there's the air pocket, the rectangular area just in front of the battery:




After tilting the bike back and forth on the stand to release the air, just one small bubble of air left (circled), the rest is now full of gas:




And back up front, the gas dropped up top as it filled in the void under the tank:




So there you go. Apparently no warped space or weird science going on, there's just a part of the tank under the seat that gets choked off as it gets filled, and thus creates a small void of air.

Yeah, I had mine on a jack stand and had to go pretty high on the jack and push the rear wheel down and even then, simultaneously tilt to the side to get the air out - gas cap on, of course, to keep from spilling out from there in the process. And even with all that, it still had that one small bubble remaining. So it would probably be difficult to get all the air out while at the pump. A good wheelie would likely do it, though.