A customer mentioned that they were bothered by the gap between the frame and bottle

so I did something about that gap.


Done.


The rear of the bottle has a recessed indent, so
it doesn't interfere with the seat tube or the bottle cage bolts on the seat tube.
This is unrelated, but there's a UCI rule that states
"the frame cannot act as a fairing for the rear wheel."
For example, between the back of the seat tube and the rear tire,
nothing harder and thicker than a credit card is allowed to pass through.
In other words, the frame cannot overlap or cover the rear tire or rear rim when viewed from the side.
If you interpret this broadly, it means sealing off the rear triangle with a membrane.
In that case, depending on the situation, even on a time trial bike
a disc wheel might not be the optimal solution.
The frame would be responsible for a significant portion of the streamlining effect near the rear wheel, so
depending on the course, a heavier disc wheel
wouldn't necessarily always be the better choice.

If you compare the images at the top, you'll see that
the bottle clearly cuts into the seat tube when viewed from the side.
If this bottle were the frame and the seat tube were the rear tire,
it would be considered a fairing—that's what I was getting at.