1. Check rudder geometry
- Pivot holes are same
- Rake is same
2. Check mast rake (dealers aren't always right)
- Sounds like it needs to be moved forward a fraction.
3. If Nacra 5.2 has a jib, try powering it up some more.
- Close the leech a bit, not too much though.

Other than that, there are a lot of very obscure alternative reasons for weather helm ranging from platform setup to sailing technique.