flavour alteration after final proof?

[Dancing4dan]

Im looking for your insight into flavour change after final proofing to 40%.

I have a 10 L barrel filled with product since mid September 2021. I pulled off a sample to proof down and taste. About 250 ml @ 124 proof before proofing it down. After proofing it down I tasted the sample over the course of three days. And I noticed that the flavour was better the longer it sat after being proofed down.

Flavour changes in the bottle for sure but this was more than I expected. The bottle had significant air space after proofing down.

Would like to hear how you proof down to drinking % and what you do to decide if a batch is finished its time on oak or in a barrel.