Put the BL2 where you usually sit and listen, watch. Really. Put it in your couch, for instance, or in your listening chair. But at the height of your head.
Then move around in front of it, close to where you were thinking of placing it, until you find where the bass sounds the best. Here your head has to be down on the floor, at the height of the BL2.
Find where you like the bass best.
That's where you want to have the BL2. The long sound waves of the bass spectrum means that there will be places where you will have little impact, and others where the bass seems to descend upon you. The above trick is somewhat influenced by proximity to walls - but when placing a sub you have to do some moving about to find where it has the best impact.