I have 2 medium/large rectangle channels that consistently do with-in a few % of each other. The slight difference in size has never made a significant difference in performance. They run in the same spot on alternating pages. I set one for "Large Font" and left the other one at "Default Font".
Of the pages I've looked at, the Large font block show ads in large font. But the Default Font blocks show single ads in Large Font a lot of the time too.
The difference is that the Large Font blocks don't seem to show 3 - 4 ads in a block at all and the Default Font Blocks do sometimes do that.
Both sets are set for Text and Image.
It seems to me that a while back G said that they will use whatever Font size they think will produce the best result on any given page at any give time regardless of the preference settings.
Anyone else recall that?