Downwash angle also depends on aspect ratio too but i assume you took that into account. I'd argue that a 1.8 and even 0.9 deg angle is not at all insignificant, certinly far from 'hogwash'.
What this means is that when flying with wings level (upright or inverted) compared to when it's in KE (wing makes no lift in KE) then the angle of attack the tail sees is different by 0.9-1.8 deg.. The difference is such that the tail has a more positive angle when in KE flight due to absence of downwash, so makes more lift (lift toward the canopy) and so tends to tuck the nose toward the belly... exactly what most models experience.

I'm sure that there are many other factors at play too but i still maintain downwash must be a significant contributor... Sadly there is not much that could be done to reduce downwash on the tail other than making the wings much higher aspect ratio or the fuselage much longer, both of which would have very negative impact in other areas.

Steve