Well, im thinking if you put it in the bottom, it won't be as apparent. that is, since the speaker is low and pointing strait, it will add to the overall sound, but not be the main you hear. On the other hand, if you go top, since its angled (and higher) it'll be pointed at you, so it should be a more noticeable difference.
So, my thoughts would be try the bottom first, see if you need more change, then go top.
also, since it's an experiment maybe you can find a used (and already broken in) older 12L. (point of that is finding one under 200, since its an expensive speaker, and the results may not be what you desire)
I like the idea of mixture because if you record, you can mic up a bunch of spots and get more sounds... and live / practice theoretically they will both add their own flavor and tone that the other doesn't have.