I believe you are referring to the 2106 form. You can either list actual expenses or take the flat daily rate. At least I think this is what you are referring.
Is it okay to take the per diem regular credit even if you are sleeping in the truck within 40 miles of your "home terminal" in transit to a drop-off? Was told I had to be 50 mile or more per nite to take credit and some weeks they make that pretty hard to do. I looked at Form 2106 and could not find any rules for truck drivers so glad someone could give some feedback, thanks.
I don't recall anything about a certain number of miles. If you are working and away from home then I see no reason to not take the deduction. You may check the 2106 instructions and see if it mentions something. Otherwise, if it were me I would take the deduction. I had an accountant tell me once that when in doubt take the deduction.