RP, here's, a system I devised that might interest you with these small fields. I took fields between 8 to 12 runners and I looked at the top part of the Betfair market.

For example, if the field had 8 runners I bet (on paper) every horse that was $8 or less on Betfair for a level bet of $1 and I did the same thing with fields of 9, 10, 11, 12 runners.

For the period I checked it (about a week), it proved profitable even when I included the favourite. But with as usual with my non-lay methods I lost interest. A bot would probably be helpful.