Policies like minimum amount before receipt don't make a whole lot of sense in a lot of cases, since they incentivize unethical people to run up the tab to the minimum as much as possible.

I've worked at both kinds of companies (receipt and reimbursement vs straight per diem based on location) and much preferred the one that handed me my per diem as cash in an envelope before the trip started. Less bookkeeping on the company's end, and if I decide to be frugal on the trip for whatever reason I've just rewarded myself with a small bonus. Seems like everyone's incentives are aligned in that case.