When the distance from the base to the rover is smaller than 20Km then "RTK fix" means 2~3cm precision.
Anything else is not an RTK fix.
If you never got 2 cm precision then something is wrong with your system configuration.
My suggestion: Make sure the system gets an "RTK fix" with a static base-station.
After you get that, move the base station without moving the rover.
If, and only if, the rover does not change it's reported location, then you can say "in UBLOX firmware 1.40+ the moving baseline option supports moving base".
If it moves then you can only say "in UBLOX firmware 1.40+ the moving baseline option DOES NOT support moving base or is NOT correctly configured".
A working "moving baseline solution" is usually very expensive, and implies serious latency constrains.
Please read a bit more about it, I think you (or I) are missing something here.