How are grace days included in Dunning Letters?

Hello!

Background info: customer lately upgraded from R 12.1.3 to R 12.2.8. We have set up Account level dunning plan and type is Days Overdue for Customer. In Dunning Plan setup 'Use Grace Days' is checked.

In Customers' Account level Late Charges is disabled, but we have set receipt grace days to 5 (just in case also in Bill To level) . In the IEX: Send Dunnings for Delinquent Customerd log file finds the grace days:

Dunning Level - ACCOUNT

cust account id - 166842

site use id - 20942

delinquency id -

org id - 165

Grace Days - 5

Disputed Items - Y

correspondence date - 09-DEC-19