George, Polyglot, thanks for your support!
That sounds like a good idea, but my next attempt will be to drive the diluted RA-4 dev to real completion. I mean at least 10 minutes instead of 2.When doing E6, weak shadows are an indication that you should run the CD longer while colour shifts (usually blue/yellow but it depends on the film brand) can be adjusted by changing the pH of the CD mixture. If I were you, I'd try it in C41 or E6-CD for the colour dev stage.
I don't have TSS, and I believe it is CD3 in the RA-4 chemistry.If you have not TSS, you can test the - CD 2, CD 3, CD 4 (chromogenic substances).
Publish them online somewhere, it is knowledge that must not be lost. I think I have the same in a Russian book, among others of course.If you need recipes Orwo (9165 or 5166/5188) I can send you.
Please see the attached image. Do you believe that more contrast in the first dev would be beneficial, or should I really increase colour developer only? The source of the uneven colour cast is unknown, since I was agitating both developers.