In most tractor type of setup airflow is not a big issue...
Pushers however have some real issues as far as air cooling goes.
One thing that will help as mentioned is the mixture and oil content.
Not knowing what your setup or engine is it would be hard to offer any real solid advice.
I would recommend that you get a copy of Andy Lennon's book "Basics of RC Model Aircraft Design", it has an entire chapter on engine cooling/cowl design, that has quite a bit of focus regarding pusher type of setups.
Perhaps you could elaborate on what type of airframe, engine setup you are using. That would give me a better idea of how to advise you on your setup.

Edit to add:
The suggestion about using a tractor prop for tuning and switching to a pusher is an excellent one, if your only issue is getting it set up...