I'm on a BA F award RT lax-LHR tomorrow using AS miles; taxes/fees are about $260. VS UC award would have been $700+ (if I could have gotten a UC award seat for the return segment, which I couldn't, other than for ORD).

IIRC this is about the right amount for UK APD and other airport taxees. IME, this is right at the bottom end of the scale for TATL premium cabin award tix. Lowest I have ever found are into DUB - and that seems to be driven by the sensible low tax policies of the Irish govt, rather than anything any airlines is doing.