I mean visible to you. Dunno about the 6 and 4, but going by some of the battles I have been in, I think that it means 64 units in visible range.
And it does suck when stuff is blipping in and out, but given the 56k speedbump, I do not know how you could expect anything different.
Although, now that I think about it, in IL2, I have had a hundred plus air/ground units in visible range.