Is the account reserve level just designed to withhold your funds?

We’ve been selling on Amazon for about 18 months now with sales growing every month.

About 60% of our revenue comes from FBA sales and 40% FBM.

Our account reserve level, as a percentage, keeps increasing up the to payout date and then resets after. At the moment, with payout due today, it’s at 60%. I.e. 60% of our funds are currently in reserve and ineligible for payout.

This just seems absurdly high to me. Is this normal? When does it stop? 65%? 70%? 90%?

When we first started it’d never hold 60% in reserve. I just don’t understand how it can be so high. Is there any rhyme or reason behind how it’s calculated?