Thanks for the replies -- especially your detailed information, Drew.
I took one full week off, then (looking back) about six weeks of reduced duration and intensity. 13 to 16 hour weeks became 7 to 10 hour weeks. FTP dropped from 282 to 223 (within two beats of same average heart rate during testing). Efficiency Factor at Aerobic Threshold dropped from 1.6 to 1.34. With your help, I think we've found my problem. It's incredibly discouraging to lose that much fitness. You can be sure that I won't intentionally take this much easy time ever again.
Last edited by FlashBazbo; 09-21-15 at 07:37 PM.