only squawking mode C?
and
have to assume the uncontrolled traffic is at the correct height? (if I wasn't squawking mode A of course which is very unlikely).
Sorry I'm a little confused. Do you mean squawking Mode A, ie I can see you on my radar, but not squawking Mode C, ie. I can't see your altitude, cos that would make more sense to me. I didn't think you could squawk only Mode C?????? Maybe I am missing something here