glum
It is not about any of the topics you mention.
It is just about thinking how the rotor slipstream will blow over the tailplane at intermediate nacelle angles and how its angle to the fuselage datum will have to be adjusted to keep its angle of attack within a sensible range. Call it aeronautical common sense if you will.
Or you could just look at any tilt wing or tilt rotor aircraft that has flown in the past or is flying today and observe where their horizontal tail is in mid transition.
It even applies to helicopters that use a horizontal tail.
As to passing on my comment to your Professor I would bet money he can't understand why nobody in your team has yet pointed out his deliberate mistake.
He is trying to get you to think!