In AH the engines of other planes are almost impossible to hear from your plane. This means that if you have 10+ planes in close proximity you might barely hear them. You have to get very close in order to hear your wingman, for example.
This doesn't seem to be a problem in the film viewer.
Okay, with these two points in mind, consider the following:
I am experimenting with sound packs. I like SOME of Mitsu's but not all of it. I really hate some of it. So I started putting some sounds back but leaving others. Specifically I am leaving gun sounds, engine sounds, and a few others.
Now, when trying this Franken-Mistu sound pack out, I found that wingmen's engines are a lot more audible, and from longer ranges! The engine of the plane I am in is no quieter than before, as well!
Perhaps the default AH sounds are causing interference with each other? Or perhaps there's something wrong with the format? I'm not sure exactly what. I'm just tossing out an idea here. This would explain why in AH (default sounds) you can't hear nearby planes but in the film viewer (which does not play the engines of the plane you're in) you can hear them.
Again, I could be totally way off but I thought I'd post my observation about the engine sounds.
The Mitsu engine sounds seem to be in 8-bit mono with 22kHz. The default AH sound is 16bit mono with 22kHz. It could be the format or it could be interference. I'll run a test next time I'm up, I'll convert the default to 8-bit mono and try that out, see if I hear any difference.