fixed machine overhead costs

Hello

can you please provide more information on how are the fixed machine overhead costs calculated for the work order. Current tests that we are running are showing that the calculation is using
Machine Actual Run Hours * Work Center Fixed Overhead Rates - with this there is no difference between the Machine variable Overhead and Fixed Machine Overhead

We would be expecting Fixed costs to apply based on the accounting cost qty.

Can you please explain the difference between machine fixed over costs and machine variable overhead costs?
Thank you very much
Best regards
Vanda de Motte
Technical Analyst Design and Configuration