I have tried 15,000, 17,000 (the default), 20,000, and currently using 23,000. And I am seeing a lot of air losses to flak. Its worse if you use auto(auto) for Req AC(Esc). But even if you set the Esc % to 25 (most cases you'll get 12(4)) there is still a high amount of flak losses for Recon missions.
In this screen shot granted there is 137 76mm and 36x 85mm AA guns but those 12 recon units should be flying at 22k and should not be easily detected. I can buy into a GA mission of 30 or more planes, or a GS mission of 50-100 getting / receiving a lot of flak losses but to me this seems excessive.
Please note that weather does not seem to matter (clear its still the same, you'd think worse weather would be harder to detect 6 recon planes).

Here the loss was 100%, 2 recon aircraft shot down?

Here is the listing of the 12 Recon missions:

It basically breaks down to:
Recon Units flown to Lost
Code: Select all
28 | 8
14 | 5
17 | 4
14 | 4
16 | 3
6 | 3
4 | 2
5 | 2
2 | 2
8 | 2
12 | 1 (seems reasonable)
2 | 1
The flak losses for Recon just seems excessive to me.