Visual and aural detecting was very important and highly developed in WW2. I don't think it's unreasonable at all for a base to be warned at the 10 mile range (actually, I believe it's 12 miles). I could even argue for dar bar to extend to the ground anytime you're over enemy territory to simulate reporting by ground troops, friendly civilians, etc.
I will also offer the personal opinion that rarely is a very large defense mounted in the short time available, anyway. If you have 3 or 4 dedicated fighters in your attack, they can usually deal with anything that gets up before it disrupts your attack if your attack plan is well coordinated and executed.
Regards,
Hammer