If the RD is at it's mechanical limit of travel yet still 2mm too outboard then:
a) measure distance on previous set-up
b) the mounting point must be examined for - thicker hanger/bracket/drop-out; misaligned hanger/bracket/drop-out
c) wheel axle to drop-out interface
a) unfortunately i don't have the previous set-up for comparison
b) It could be a thick hanger... it's a Chinese eBay frame.
c) wheel axel is sat nicely and the wheel is perfectly centered
If the RD is at it's mechanical limit of travel yet still 2mm too outboard then:
a) measure distance on previous set-up
b) the mounting point must be examined for - thicker hanger/bracket/drop-out; misaligned hanger/bracket/drop-out
c) wheel axle to drop-out interface