How can the system be configured so that future dated leave applications will be reduced from the current period's leave balance?

This feature is available on all Deel Local Payroll powered by payspace payroll editions
To have future dated leave applications reduced from the current period's leave balance, enable the "Force employee's leave balance to reduce in current period rather than start date period" checkbox under the Leave Calculations section on the Leave Settings screen.
Navigate > Config > Human Resources > Leave Administration > Leave Settings > Leave Calculations