(By the way, if you mean Angel of Marksmanship, that's AoMr. Considering there's also AoMs (Masochism) and AoMC (Max Carnage), it's good to differentiate.)
Other than special levels (example: Hell's Arena) the floors are generally randomized. If you could provide a screenshot or, at the least, the type of map it was (Maze of Rooms, Hellish City, etc), it would help this discussion greatly. I'll ask if there happened to be water/acid/lava in or around that T-hole, as this can be the cause of some irregularities in the map's typical layout. In addition, based on my knowledge of maps, it is possible for the more crowded maps to contain thicker borders (usually reserved for the Maze type).
There's a possibility that something was randomly lodged into that small region, but I highly doubt it would be particularly more useful than the other items that spawned with the level.