A couple of squaddies and I tested this.
If enemy dar up....you WILL show at 65 feet. If enemy dar down, you will NOT show at 499 feet.
Now for the weird stuff...If you up from your base and no active enemy radar is there to track you, you can noe old school in your sector and the next with ease.
We had noticed that after you start an noe in any given sector from where you lifted, you can climb to several thousand feet and show no DAR.
This works till you hit the next sector then the DAR BAR pops up. Still working on whether or not that works with the enemy base in same sector.
But the general answer to your question is There are Quite a few more cons in some sectors than the dar bar will show. Must be a glitch, dint know