Here is the plain math. A buyer that already wins more than half the policies sold in a given year does not need to stretch on any single case. It can bid at its target return, lose some deals, and still lead the market on volume. Smaller buyers that need to build a portfolio often have to bid harder to win the same policy.
That is not a criticism of Coventry. It is what market position does to pricing behavior, and any buyer in that seat would behave the same way. It is also the entire reason competitive bidding exists.