It's not 'flat' that you should be paying attention to. It's 'flattened down' that you should, and there's a difference. It doesn't have to be 'flat' to be
Machine Doubling. What you have is the effect of the die bouncing on the minted coin, hitting it again. The letters that were originally minted at the right size and shape are now half 'flattened down' because of that second hit, and now don't have the right size or shape.
A doubled die will actually ADD TO the size and shape of the letters because there's more than one single set of letters on the die itself.
I still recommend to ANYONE having trouble with the difference to buy a doubled die so they can see it in person. Without doing this, if you're confused - you're wasting your time. It could take years to 'click' without seeing it in you own hands.