Ordinarily, the downwash angle at the tail is related to the lift coefficient more than to the wing/body AoA. Would your values be more specific to a stalled swept wing?
If you ignore the slight complication of no-lift angles and wing body settings (which change the zero body angle downwash), then lift coefficient is just AoA times lift curve slope, so they move together. Almost all textbooks and reports use the AoA format as this makes the equations a bit easier to handle. I guess I just stuck with it from force of habit
The numbers I quoted are pretty good for an aircraft like the A330, at least up to stalling AoA. When lift curves go nonlinear then I would agree with you that lift coefficient would be a better handle. I don't think anyone knows exactly what the downwash would be at 60 deg AoA, but I was using it in an argument about THS stall and as the later bit of my argument took the THS away from stall I didn't worry too much about it
Thanks for the welcome!