HRA contribution calculation following mid year change in coverage

[waid10]

Hi. How do you handle the contribution calculation for an HRA when a participant makes a mid-year change in coverage?  We (the employer) provide a $1,500 HRA contribution for Employee + 1 (spouse or child) coverage and a $750 contribution for Employee Only coverage.  We have a participant that changed from Employee + 1 to Employee Only coverage on April 1st.  Is the calculation simply pro rated for the remainder of the year?  

Here is an illustration of my thought process:

$1500 divided by 12 months = $125 per month for January - March = $375.00

For remainder of the year, $750 divided by 12 months = $62.50 per month for April - December = $562.50

 $375.00 + $562.50 = $937.50

Is this the correct approach?