hi
betfair api only have a maximum of 6 last starts, so there is no way of knowing if the selection has more than 6.
you can use the last 6 starts and calculate the place percent from them.
or you can look at the racing post , then find the selections with more than 20 runs and have 33% place.
then make a list and input them in mfp, then use the trigger for the price condition.
mcbee