The crossover issue might be due to incorrect color balancing your film exposure itself. Ektar is much more sensitive to color temp issues than traditional color neg films, and warming filters are sometimes needed, but the payoff is much cleaner vibrant hues. I'm getting Ektar shots
on CAII which are so clean and vibrant that I'm afraid people will accuse me of cooking the saturation and saturation in Photoshop, even though the original scene actually looked like that, and I don't use any kind of digital technology in my workflow! I have been using both Kodak RA/RT chemistry and the Arista branded substitute, one shot in drums, and the results are identical. I can't address homebrew RA4 issues. The color balance difference between Super C and CAII were less than 5cc's of green for me - that's all the "digital optimization amounted to - a tiny bit more green sensitivity due to the relative weakness of green lasers. I took me less than half an hour to recalibrate a master neg. Masking is quite easy on 35mm, but would involve an extended conversation. I had to learn a lot of this stuff the hard way myself, and am currently printing CAII several times a week, mostly big prints from big negs, but it's all relative to the degree of magnification. A 5X magnification from Ektar sheet film, for example, will yield the same color saturation and contrast as a 5X magnification from 35mm, all other things being equal (which they are, because I always initially calibrate to a precisely exposed neg of a Macbeath chart,
and keep these master negs on hand for various films and formats). There are some "room temp" or "variable temp" RA4 "mono" kits I've tried
that I was seriously disappointed with, so am aware that distinctions of chemistry can be a game changer.