Yup, 1 - 1.2mm would be optimal.

The problem with these small EDF's is that often the shroud is glued in and out of round. The material is not very stiff and easily deformed by hand.

So 1mm on one side of the fan blade might mean 2mm on the other...

That is why it is important to run up the fan and look for any rubbing areas, and work from there. If the fan rubs too much the motor will build up heat ( the friction prevents movement ) and it can overheat or overdraw the ESC... IN THE AIR!

Once the clearance is established, the fan should then be balanced, re-installed, and another search done to see if there are vibrations or rubbing issues.