I honestly believe, the word "reserve" is not that important here - the crux is, you do not pay the entire rental cost to the rental car company DIRECTLY with your MC, if I understand correctly.

As for discount and coupon promo with rental car company - it does not affect the coverage. In the case of our claim, there was a 20% discount code being used and MC did not blipped. In fact, once the paperwork was in place, the adjuster wanted to pay the repair estimate right away, before the rental car company submitted the Fleet Log for the Loss of Usage claim. I was naive enough to ask him to wait, and tried my best to get the Fleet Log. The Fleet Log was shot down for reason of "not enough detailed information". We ended up paying the combo of Loss of Usage and Admin Fee for a total of $320 after bargaining it down from $450 with rental car company's insurance agent (It was a Franchaisee and its insurance matter was handled by a 3rd party).