Unfortunately there is no way of telling the exact distance a enemy is 'leashed' - SE's belief seems to be that the player would fight them where they're found and not 'pull' or 'train' them across the map, which is the whole purpose of the mobs being leashed in the first place (it's to stop old FFXI-style exp parties camping enemies and then pulling them vast distances to safe locations to fight for exp, as you're expected to level in this game by other means like quest completion and FATEs).

Either way, that particular enemy is probably to act as a 'guard' for the other two rooms, as you have to clear both side rooms to get the firesand to open the way to the boss - you're meant to wait for it to arrive in the centre and fight it there instead of just ignoring it and jumping to the room or pulling to somewhere else. Either way, if you're doing it at a low level it's best to hang back and wait for it to scurry into the centre area and kill it there.