Star Trouper which was around 14/1 top price earlier, and which I actually laid @ 12.5 has been given a deduction factor of only 0.7%. Yet Benenden which was a 66/1 shot and trading at about 80 on the exchange has a deduction factor of 1.3%.
I pointed this out to Betfair via chat. Was told the the "Traders" would look into it. Nothing seems to have been done about it. Only cost me about £30, but obviously cost all layers of that race thousands.