Let's start by considering that all angles that matter for flying are related to the wing.  The fuselage is just along for the ride and to hold the other bits at the angles they form TO THE WING.  Nothing else matters than the relationship of the thrust to the wing and the tail to the wing.</p>

So now someone wants to correct a ballooning problem by reducing wing incidence.  But consider what it's doing to the thrust line to wing angle.  It's LOWERING the angle so by reducing wing incidence you're also reducing the downthrust angle by the same amount..</p>

As for the downthrust angle acting on the stabilizer I'm afraid I can't buy that one.  It may be a factor but I've seen far too many planes that fly where the prop wash doesn't flow past the stabilizer .  Also a plane in flight is flying with little if any propwash passing the tail since at speed the prop is lifting or screwing it's way through the air unlike the ground based propwash.  So propwash at speed is going to be reduced to an amount that is proportional to the prop's slippage rate.  Typically maybe 15 to 20%.  And what about pylon mounted engines?  Or models with T tails that have the stabilizer well up out of the prop's thrust line?  And then there's pusher designs......  Nope, the thrust line angle works by producing a torque that acts on the wing due to the geometric thrust component that is not in line with the wing's airfoil.</p>