From: PDX (and now) London, UK
I don't know how many layers are optimal, or even if there is an optimal number. It seems like more layers is better (but I do not mean that in the strictest sense), so put as many as you can with what you have. It also seems that you do have to have enough defenders (quantity) to drag the sweepers into that lower altitude fight that you want, which of course will include some defenders getting 'the dive'.
I've had good success with layered CAP with inferior aircraft, and so has Andav (curse you! ), my current opponent.
I can say without any reservation that pilot experience and skills do make a BIG difference. As far who gets 'the dive' and when, I don't even bother to watch that. I hit the Esc key and only care about the outcome of the combat. Adjust what you are doing (altitude, training, etc.) to get the combat results. Forget about 'the dive'. It'll drive you nuts.
With the 42k P-47 sweep all planes get dived on, so the top and middle and bottom layers suffer from the outset, and the numbers get massively extreme, up to 15:1 even with the best pilots in the best airframes available. Then when you multiply that by several months, years, you get a pilot quality discrepancy that is massive.
As stated above the 32k max HR we're using now (after having used 2nd best maneuver) has worked very well since we tried it out. With a massive set of sweeps the Allies still get 2-3 to 1, but not 10-15 to 1 anymore. Generally the lower levels of CAP are hit, but the upper layers do fight it out, and sometimes they get to dive into the lower sweepers after their dive. It was hit and run for the faster Allied planes so it does make sense that it's hard to get to the lower ones after they dive. This HR though does make the upper layers, with good piot sand the best frames duke it out a bit. That's good for the game and makes both sides continue to parry, thrust, deceive and surprise, which is where it gets fun!
"Success is the ability to go from one failure to another with no loss of enthusiasm." - Winston Churchill