dobbin,
I did not check if this works well, so try it in test mode first:
Trigger File has 2 Back bets, executed only once per market.
Back Bet with shorter odds (=stake 70) has condition:
selections back price is minimum
Bet with higher odds (=stake 30) has condition:
selections back price is maximum.
As there are only 2 selections enabled for auto trading due to your import, and minimum and maximum is restricted to selections enabled for auto trading, this might work for you.
But you should add additional conditions to forbid the trigger to enter a bet in a "strange" market. At least
markets Back Book % is less than 101,
and Every Selections back amount sis greater than 70
should be added in BOTH trigger actions.