arxipov,
Not specifically familiar with EU ops but and the all the information I am about to provide is from the Australian context.
So far as I am aware, visibility and RVR are not the same thing. The formula you quoted and used, is the standard formula for calculating visibility. We all know that the quoted visibility must be enough for you to see the landing area or start of the lighting system. This is not the same as RVR but you appear to be using the terms interchangeably.
In Australia we only publish RVR's for precision approaches and they are standard depending on the DA. They are not individually calculated for each scenario.
I have no idea if this helps....but I think you are calculating one thing and trying to apply it to something different.
Someone more familiar with EU ops will be along shortly to clarify, but that is my suspicion of your problem.
Alpha