Does campaign diff settings affect encounters?

[theteabag]

Ive been playing nearly the entirety of the Stalingrad campaign without ever encountering He-111s. I only ever see 109 variants and Stukas. Ive set difficulty to easy and frontline density to medium. At what difficulty do I encounter the heavys? Also what else do those settings affect?

[LukeFF]

The difficulty setting controls the relative skill level of friendly and enemy flights, how many enemy planes you'll encounter, and how many AA guns defend a target. 

[Feathered_IV]

I’ve forgotten the details, but there is some sort of limitation with the career programming that prevents some aircraft being generated if their home base is too far away.  The bombers and transports are the ones that are effected the most.  Hopefully this gets improved by the time the Normandy career comes out, as the flight times are going to be much longer there for many units.