hi
as pcal72 said , Example the price may give a huge jump, between triggers firing and bet placement by betfair api.
the trigger sent the bet at 1.16 as it should have because the condition is when the back odds is between 1.10 and 1.20
BUT just before betfair received the bet the price jumped to 1.34 , so betfair gave you the best price available.
IF the price dropped to 1.10 the bet would have been unmatched at 1.16 .