I keep answering this question about range on the 319 and 320, but here goes again. The 319s have 22k engines and the 320s have 27k engines, yet the APS weights of the 319 is only about a tonne and a half less than the 320 due to the different centre fuselage section with the 2 overwings.
The reason therefore that the 320 does the longer routes is the take off performance, usually at the other end but occasionally out of UK. I did the sums for a 66k and 68k 319 on a LPL-TFS-LPL, and with a typical Canaries pax mix and all the holiday baggage it was very marginal due to performance limited take off weight - the 320 with its extra thrust eats it.
The 320 could be a bit limited even from MAN going to SSH with all the scuba gear, but seems to have gone OK so far, the 321, those left, are better on this due to even more power, but are all at LGW.