The COX line of planes, other than the PT-19 were not suitable for rank beginners with no additional assistance to have any reasonable level of success.
The fact that COX included fuel that was marginal in performance for the engines wasn't helpful either.
Higher Nitro fuel was a big part of the success formula. Missile Mist was my preferred fuel of choice and sometimes I got some Fox 40-40 that made the engines perform much better.
All of the things you mention for success were not automatically known. You needed someone to tell you or learn from trial and error.
Sparky