Himring

[Aiwendil]

It seems to me that Maedhros actually had a fairly good position on Himring. From "Of Beleriand and its Realms":

The chief citadel of Maedhros was upon the Hill of Himring, the Ever-cold; and that was wide-shouldered, bare of trees, and flat upon its summit, surrounded by many lesser hills.

So the terrain surrounding Himring was very hilly and probably quite rugged; Maedhros may well have had rangers patrolling them, or even forts or other defensive structures hidden among them. Himring itself could probably be defended quite well by stationing troops in a circle around its summit. Maedhros would have the advantage of high ground and his archers would be in an excellent position. Also, we have no idea how extensive his fortifications were. There may have been outer defenses on the slopes of the hill.

Of course, regardless of his situation on Himring, Maedhros was in a difficult spot after the Bragollach. The passes on either side of the hills, which his brothers had previously held, were taken in that battle, and he could be easily surrounded. Perhaps if Morgoth had launched an intensive assault Himring would have fallen. But Morgoth did not. I don't think that Himring itself mattered very much to Morgoth's strategy in the east at this point. What he wanted in the Bragollach was to open a pass into Beleriand; and he accomplished this by taking both the Pass of Aglon and the Gap of Maglor. Unless Maedhros had the power to really harass any Orcs coming through those passes (and apparently he did not), capturing Himring itself would have been unnecessary.