How to set sample time properties if the model's fundamental sample time is slower than sample time with highest priority?

I want to run my model with multiple sample times with a fixed step solver. So, I chose periodic sample time constraint as 'specified' and defined the sample times properties in the order of lowest to highest sample time with priority highest to lowest. Blocks with sample time 'inf' or '-1' now have sample time which has the highest priority, but I want these blocks have fundamental sample time. Can anyone suggest me how to define my matrix under sample time properties? Thanks in advance!