I take your point re. the Avios value!
I also agree with what you say re. demand. Presumably BA feel there is more demand during so-called peak periods. This would explain them charging more cash for flights on those dates. However, I still don't really understand their logic in charging LESS Avios for peak redemption upgrades. Surely if there is greater demand they would rather sell seats for cash than encourage redemption upgrades?
I think I was a bit garbled in post #63 (was thinking about lunch rather than what I was typing).
If the underlying cash fare in WT+ is (on aggregate) higher during peak periods, then having a lower Avios charge to upgrade to CW is understandable. It's the overall 'revenue' (cash+Avios) that's the key - so on-peak, even with a lower UuA amount, this might equal or exceed that for an off-peak cash fare (low fare + higher Avios UuA charge).
There's also the fare bucket angle. Perhaps revenue management release far more T (discount WT+) inventory off-peak than at peak, and this is a crude way to charge more for upgrades to CW which come from T rather than E or W?
TBH, the amount of noise everyone made about what amazing value UuA was, it was only a matter of time before BA enhanced it.