Richard Migliore on XBTV yesterday suggested that the success of frontrunners had more to do with kickback than with footing.

After walking on the track, he and Zoe Cadman both said that, at least late in the card, inside was not the place to be. Of course, the jocks seemed to know that. The inside horses were not right up against the rail.

Regarding speed biases, four possible causes I can think of (without any supporting evidence) are kickback (as above), wind, the ability to choose your path and footing that is favorable to horses with a quicker stride.