Watercolor Paper - Radiant White? I don't have the same problem. What is the ambient humidity in your area? Here, it's about 14% so the paper is quite dry when the ink gets to it.
If humidity is part of the problem, you might try letting the paper sit in the room air long enough to stabilize at the ambient humidity before printing. Perhaps this would help keep the surface dimensionally more stable. Just a thought, I have no idea if this would work for real...
I'm not sure if you are asking me too, but I'm printing at 2880x1440. I can see more fine detail at the highest res setting and at the high res setting the dense colors come out a tiny bit richer, particularly on matte papers.
The high res setting is supposed to lay down more ink, but it can't be too much more or the colors and desities would come out wrong.
I have had thin, matte paper come out rippled right out of the printer, but even my cheap Epson Photo Quality Inkjet Paper dries flat for me.
This may sound kinda goofy but it has worked very well for me.
Take your print and lay it to dry on a table with a paper towell roll (or similiar) underneath allow the print to dry curved and then check for ripples. I had the same problem and after this technique i have had NO problems. ....