Most people these days mount the regulator after the carb. The recommended mounting method changed about 20 years ago but I'm not fully sure why. I think the carb guys decided that it was just better to always be circulating fuel by the carb rather than circulating the fuel between the regulator and the tank and leaving stagnant fuel in the pressure line between the regulator and the carb.

I've seen both routings work just fine but the full circulation model probably works in some situations such as really high heat, where the stagnant fuel model has problems.