I read on a professional comedians website that if the audience are talking but half-listening to you, get quieter, than they’ll put their full concentration into listening to you.

I agree. When good comedians get “heckled”, it’s almost always someone who’s talking to their friends too loud, not really heckling. It still has to be dealt with, of course. If they have a real heckler, the person is probably drunk. But these should be rare occurrences. Someone who gets heckled on a regular basis probably just isn’t funny. They either need to quit comedy, or radically change their act.