Mid-period costing changes - will elements be costed using the old or new costing?

Summary:

If employee costing is changed mid-month, and no proration event occurs on that date, will the payroll costing use the old or the new costing for that element?

Content (please ensure you mask any confidential information):

Scenario - a monthly paid salaried employee, has their costing changed at position level (the level shouldn't really matter) on 15th June. Costing changes don't trigger a proration event. No other changes occur on the employee that would trigger a proration event. This means the payroll will calculate a single value for the salary covering the whole period.

What is the expected costing result? It won't split the costing because there is no proration event.