I'm with you 212, idle on all the types I'm rated on (Engineer) is an N1 control function, haven't worked the 135 for a few years but I'm pretty sure it is the same, you may well get 60% N2 but as you say the N2 will slow if the collective is raised and of course no longer indicate 60%.
Can you do a rotor braked start on the EC135? like other models? If so then this proves the governed N1 control at idle.
FS