CraterMA is a small map but has 120 fields, more than any other small map. However the point is not so much how many fields but how long the front line is. Generally there are just 4-5 enemy airfields near to your country's fields on each front line on this map. I reckoned that was the best figure, more than that and the action gets too spread out at off peak times. Less and it gets too stagnant, playing the same few fields all the time.
I think the reason there was less than the normal amount of air activity was that there were more players in TT. Lusche posted a thread where he said the ratio of kills was 60:40 GVs to aircraft rather than the other way round as in most other maps. I'm hoping this is a temporary phenomenon and things will settle down after a few cycles. Another thing I noticed was that a lot of the air activity was concentrated on the coast rather than through the border mountains. The border mountains on this map aren't the barriers you find in Trinity or Beta2 however, the valleys that run right through them are typically only 2k high.