Not sure if this will help, but when I had to place my VP150 below the tv, I turned it upside down from previous installation (flipped the front grill to look right side up) and this angle up seems to be working fine. Just a thought and not sure if that is how you installed it or if you just moved it from above to below as it was.
I just saw your comment and the Axiom Center Speaker Placement video
I think this will work for me, but I have one question. After flipping the speaker, the women in the video says the tweeter will be upside down. She then proceeds to remove the tweeter, turn it over and reinstall. Is this necessary?