On a decent aerobatic design , One can setup a cruise speed and trim hands off then roll to inverted and add what trim elevator necessary to again acheive level hands off flight.
the minute trim change indicates that typically the DIFFERENCE in AOA for the wing is well under one degree.
remember one degree is 1/4" in one foot.
I would venture that any downwash to the tail is of little or no consequence
I guess someone could calculate the exact angles but I would again venture in this case, the error percentage is close to the calculation.
As speed decreases or wing loading increases, the angle will increase - that's a given. I frankly don't think downwash is any kind of a factor in this situation.