I have watched some of the last couple of shows and found them unfunny (but usually like LB).
Seems to me that a vile character (like Vickie Pollard say) at home in England in a sketch with other English (British) people works very well.
We are laughing at ourselves I suppose.
But a character like her set in the USA with USA people is just not funny because we are almost embarresed by her behaving like that in another country.
The USA actors watching these characters (even Matt Lucas or David Walliams when playing an American) seem to sit there open mouthed at how awful they are.
So when they are set in the UK we are part of the joke, so can laugh openly, but set in the USA we just sit there and squirm.
Just my analysis anyway.