Depends on how do you write the bet size and the bet's type.
In general for back it's back_size, for lay it's (lay_price-1)*lay_size
For example you lay at min_stake + last_lost then condition should be
AND Trigger Expression (lay_price-1)*(min_stake + last_lost) is less than IF(test_mode=1,test_fuds,real_funds)