Here is the answer I found out at my own cost, at least this is the only way I could properly set up low action. The key was the angle of the bridge!
I've been having issues with the EZ II since I purchased my Jem, and I even thought about reselling it as I suspected problems with the neck. No matter how I adjusted the truss rod, I always had fret buzz either on the low or on the high end, so I had to compensate by lifting the bridge. I was very surprised, because I also own a Jackson - quite a cheap guitar in comparison - on which I never had problems with setting up low action, even without ever adjusting the truss rod.
Then it came to my mind that since the frets are curved, the bridge must also provide some curvature through the strings, meaning that the two E's are slightly lower than the G and the D strings. This difference is hardly noticeable with the naked eye, at least not by just looking at the bridge.
But this is exactly why these bridges are designed in a way that there is no 100% accurate angle setting on it that suits all neck dimensions! This seems like a clever design feature, and you have to adjust your bridge angle in a way that suits your neck. And this angle may be different on an RG, compared to let's say an S or a Jem.
I have found two types of explanations on the web and also on youtube, one stating that the top of the bridge must be parallel with the body, the other stating that the bottom of the bridge should be parallel. In my case neither was true. By adjusting the spring tensions I tried both configurations, but none was satisfying. For a while I had the top parallel, then I switched to the bottom being parallel, but still could not set up low action properly. So I strengthened the springs again just a little, like 3 quarter turns with a screwdriver, then re-tuned the whole guitar.
Now my bridge angle is exactly between the two mentioned extremes, neither the top, nor the bottom is parallel with the body.
So to summarize it: by adjusting the bridge angle you are effectively changing the string heights relative to each other, sharing a horizontal curvature provided by the nut positions (set up for correct intonation) and a vertical curvature provided by the nut heights. This angle should be set in a way so that the string heights perfectly match your neck's radius. Your only option is making small adjustments to the bridge angle, and check how it affects low action and fret buzz, but beware: the more the bridge is angled towards the body, the more your string heights will follow the horizontal locations of the nuts.
I am not sure how much is visible on this photo but I am adding it anyway:
You can even see it on this photo that the nuts towards the middle are slightly higher. But if the whole bridge is angled towards the body this vertical height pre-set is ruined by the horizontal intonation adjustment position, so your strings will have incorrect heights relative to each other.
So here is a very brief summary: the angle should be anything between slightly angled towards the body to completely parallel with the body, you have to find it out yourself which will match your neck radius better.
After further experimenting I've finally ended up with a bridge angle where the top is almost parallel with the body, because this allowed me to further lower the action without any fret buzz. Now the strings are as low as on my Jackson. Again, don't forget that this is a Jem, which may have different neck radius compared to an S.