Thrust angles are used to counter a plane's tendency to climb, dive, or pull to the left due to torque reaction. What you add in terms of up, down, or side thrust will vary from plane to plane. Most kits and ARF's will have the firewall canted for what that plane needs. If you need more due to modifications, you can place washers (different #'s of, or thicknesses) behind the engine mount at the appropriate corner(s) to change the thrust angle. Sometimes the different mfg's take different approaches to correcting flight tendencies.

As an example, I have a Hangar 9 Cub (80 inch wing)ARF and a 1/5 scale Sig Cub (84 inch wing). Both planes are very similar in size and basic flight characteristics. The Sig has downthrust and no side thrust built into the firewall; the H-9 has neither, but the incidence of the tailplane is much more positive than the Sig, which will tend to keep the nose "down" by keeping the tail "up" in flight. The Sig does the same thing, essentially, by having the thrust of the engine pull the nose "down", opposing the tendency of the flat bottom wing to climb under power.

Most planes with flat bottom wings will benefit from a little down thrust. and most all will benefit from a little right thrust.