Is a threshold at 70% of target defensible when half the team falls below it?

Commercial insurance broker in the UK, 90 producers. Our new business bonus has a threshold: nothing is paid below 70% of the annual new business target, then it pays from the first pound once you are over. Last year 44 producers finished below 70% and received no bonus at all.

Management reads that as the plan working, since poor performers are not rewarded. I read it as half the team having no incentive from about September onwards, and the targets being set as wishes.

What proportion of sellers would you expect to finish below threshold in a healthy plan?