Well, I can tell you my experience as a USA expat (and former waiter) who always used to over tip (for Colombia). Worse, I am married to a Colombiana who hates when I over tip.

I love the standard propina.

I always get asked if the propina should be included on the bill before it is presented to me, so I do have the option to refuse. I never have refused, or had any reason to do so. With the standard propina, I now feel OK with only tipping 10%, my wife is OK with it, and, so far as I know, the server is happy. There have been a couple of occasions where I handed over a few thousand extra pesos for extraordinary service.