What is the maximum length that the shaft stub can be if the mounting bell is fixed directly to the application?

If the mounting bell is mounted directly on the application, i.e. without an additional mounting bracket, the length of the drive shaft or shaft stub is limited to a maximum.
In the picture below, this case is shown with a mounted encoder with servo flange.
The distance between the flange of the encoder and the surface of the application is 25.85mm.

If now the usual length of the encoder shaft, which is 10mm, is getting subtracted from this distance, there is a distance of 15.85mm between the surface of the application and the encoder shaft.

Since the encoder shaft and the drive or stub shaft must not touch each other, the drive shaft or shaft stub should not exceed a maximum length of 15mm.