When I was in my teens my father and his friends would tune a channel and plan lunch at Fredrick Md. during regular Saturday club flying. Before that they would give a common location to group up which was code for fly around chasing each other's 6 over a well known farm. If it was partially cloudy, you could miss everyone while looking between cloud gaps and end up with one of them sneaking up on your low 6. If it was a clear day, 5 miles was a good average distance to see them coming. 10 miles, maybe if something large and Military was flying around at 10,000ft. All of our antics was between 7 and 10k. Once you saw something, it was hard not to keep your eyes on it. But, until then, you could miss small planes for many reasons even on a clear day. That is why my only task was to keep scanning for other planes becasue the Maryland airspace was very busy with private aircraft. Lower planes unless they were all white blended in well with the Maryland countryside.