HI SMALL RC! Check your rudder linkage to make sure that it can't wimp out, especially in push mode. A plane that has a small rudder might not have the authority to stop the planes' momentum. Ample rudder area above and below the fuselages thrust line is helpful for inducing, and getting out of flat spins. A goodly amount of rudder throw will help also. You might think about installing a larger rudder, even counterbalanced per whatever proven example you can use to get an idea of proportion. Those flat spins are fun, huh? Setting up your ailerons to act as flaperons when coupled to the elevator will flatten those spins out even more!