Very inconsistent. A month or so ago, I ran into a sector that had zero dar bar. About ten seconds after I crossed the grid line, I ran into a pack of 5 or so enemy aircraft above 10k.
A couple weeks ago, I was headed towards a sector with no dar bar on my screen but a teammate was telling me he had a dar bar in the same sector. Now, we could've been looking at two different sectors but I think that's doubtful given the situation at the time.