dino.. Do you really work a lot on room placement with bass gtr? With gtr and drums the room can be everything but I've always just close miced bass and blended the DI.. Do you use room mics?
I usually have my bass cab mic around 1 to 1 1/2 ft from the grille. If the room is untreated things can get a bit nasty. I always end up moving the bass cab around since I don't work on big rooms often. Even if the player is balanced and the instrument properly set-up, you can hear many room related inconsistencies as you play the first couple octaves. Bass response in smaller rooms is a bitch. You may have the mic in a hot or cold spot easily.
With guitars and drums rooms indeed make or brake the sound/tonality etc but whereas electric bass tone is not that much affected by the room, it's all important low freq response is. You may have some comb filtering on the 800Hz-3500Hz region of the bass and it doesn't falsify the sound [much of which is masked anyway, he he] whereas a lumpy freq response captured by the mic can result in heavy EQ'ing to tidy things up later.
I don't use room mics for the bass. I might do it if I want to blend just a bit of natural ambience to a sparse arangement but the room mic will be radically processed to avoid bass problems when blending with the close mic.
Use a big, treated room for bass if you can but don't get too worried on this - a balanced player on a well set-up instrument going through a decent valve amp is 90% there...