With a 50/50 driving mix I get 21 mpg with my 98 T5 (with
a manual transmission). That was done driving mellow. It
would drop to 19 mpg when driving "sporty".

I currently drive about 90% highway and get 25.4 mpg (my trip
computer shows an average speed of 45 mph). Do you have a trip
computer? It might be interesting to compare milage to the car's
average speed. I would think higher average speeds would indicate
more highway miles and people would see higher milage.

You might double-check air pressure in the tires since that
can make a difference.

Your other posts says you recently tuned it up (plugs, etc.).
Has the milage dropped since the tune-up?