I think what he means is that the mast is only tall enough to allow the boom to be about 7 feet above the tower leaving about 2 feet of elements extending down below the top of the tower,not really inside the tower. I may be wrong. If I am correct you will be OK. I ran such an antenna with about 4 feet below the top of the tower and saw no differance.Of course flatside won't be affected anyway and if yoy extend the mast then the mast itself will be in line with the vertical elements.The differance between the effects of the mast and that of the tower are minor.Just try not to have the boom at the very top of the tower.