How to split absence balance entitlement between multiple assignment

We have qualified entitlement plan where we have created a entitlement fast formula based on the Length Of Service of the employee. We see its working as expected if employee has single assignment but when employee has multiple assignment we would need to split the entitlement based on the FTE.

For example if employee works 2 years their entitlement is 300 hours.

so the employee with single assignment will get 300 hours & the if the employee has 2 assignment with each assignment FTE as .5, then the entitlement should show 150hours for one assignment and 150 for 2nd assignment.

Is this possible? Can anyone help.