I am receiving short term disability, the math doesn't add up. My company is basing my pay on 36 hrs per week? How should it be calculated?

I am receiving short term disability, the math doesn't add up. I have worked full time 40 hrs a week plus for the 7 months since I've returned. My company is basing my pay on 36 hrs per week? How should it be calculated? Doesn't it go based on my true hours worked? They pay 60% and I make 18.00 per hour and work 40 hrs. plus weekly.

I don't believe my short term disability payment amount has been calculated correctly. Can my employer just choose an amount of hours per week to base my pay on, or is it calculated by actual hours worked.