Indeed full scale airplanes are rigged to climb at full throttle so the pilot doesn't have to pull the stick back for 20 minutes while climbing to cruise altitude. Our models absorb a considerable portion of out attention just keeping them within visual range. Thats why they are rigged to be altitude neutral with throttle setting. While your comments on full scale craftareinteresting Buzzard it just confuses this discussion. Lets try to use R/C examples ok?

Let'sdesign a very simple .60 size low wing sport plane. It will weigh 7 pounds, with 60" span and 11" constant chord. I will make the stab parallel with the fuselage angle for simplicity. It will use a NACA0012 airfoil. I want it to be altitude neutral at both half throttle (V = 50 mph or 73 fps) and full throttle (V=80 mph or 117 fps). How should I rig it?

Weight = Lift (full throttle)

mg =( Cl ) A (r) V^2 (1/2)

Solving for Cl at full throttle, Cl =2mg/rAv^2 = 2(7)32.2/(.0745)4.58(117)^2 = 0.097

Looking this up on a lift chart for NACA0012 we discover a Cl of 0.1 corresponds with an angle of attackequal to 1 degree.
We now know that if we want the fuse straight at full throttle the rigging needs to be ( ,+1, 0). We still don't know the thrust angle we need so it is left blank for now. We could easily tune the plane at this point through trial and error by simply adding a degree of downthrust at a time until it flies level but we can still get closer before we have to get our hands dirty.

Weight = Lift right? so, Lift (half) = Lift (full) also. Writing the lift term for each throttle and speed setting we find that all the constant terms drop out and leave us with a ratio:

Cl v^2 = Cl v^2 so, Cl(half) = .097 (117^2/73^2) = 0.249

Again, looking this up on the NACA0012 chart we see that a Cl of 0.25 corresponds with 2.5 degrees angle of attack. So we're only talking about 1.5 degrees difference in the angle of the fuselage between half throttle and full throttle! We could do a free body diagram and determine the lift generated by the stab, thrust relative to the throttle setting etc but its probably easier to just go the field and start at (-2, +1, 0) and change the first number up or down until it maintains altitude at full throttle.