I recently set up a NR on my new Frankencilo build (13-21 + 42-53). I have no need for the big-big combo so I set up the chain for the 53-19 combo. I also have no need for the small-small combo and my chain tension is fine on the 42-15 combo.
On initial assembly I noticed the RD was misaligned - apparently the bike had fallen on the crankside in an earlier life, so I had to tweak the hanger gently back into alignment. You might sight the RD from behind when mounted and see if that's part of your issue.