Has HTC changed the dar bar to only show when you or friendlies are flying within a certain range of the enemy? Or am I just going crazy and just not seeing the dar bar on map?
I don't think there are intentional changes in the way the darbar works. What you just noticed are irregular glitches that do happen. We (Rolex, me, and someone who's name I can't remember now

) did some extensive tests on Mindanao the other day.
While basically working as usual (darbar at 500ft), we had significant discrepancies between our frontends. A friendly in the next sector did not create a darbar for me, but for the guy flying next to me, and not only for a few moments. I could run into an enemy at altitude with darbar only coming up a few moments earlier (no, no one of us just crossed into sector), but I can see darbar by single enemy cons many sectors away, behind the frontlines.
Not too long ago, an enemy mission was called out inbound to our field on Mindanao. As there was almost no darbar, everyone expected them to be NOE. When I finally encountered them, a full length darbar suddenly appeared and I had many buff formations overhead at 5k!
I wasn't the only one, there was quite a lot of "WTF?" and "How did they climb that fast" on countrychannel.