The tapered collet will compress over time a little and the distance will get smaller. If you have tightened up a prop on the shaft yet either this could be a partial cause of what you are seeing too. The collet and drive washer are pressed together on a taper. The tighter you make the prop the more grip the collet has on the thrust washer and also the shorter this gap is that you are referencing.

Try taking the thrust washer and collet off your 160DZ and put it on the 170 and the spinner gap should be the same as before.

This was not a change that I know of in fact it is just probably a difference between the new collet and an old one.
There is not a new version of the collet. I know YS has made some changes in recent years to provide a more aggressive grip pattern on the front of the drive washer....but that is the only change I am aware of at this time.

1mm is pretty small difference....

For safety, and for the sake of your model you should at least have a spinner gap large enough that it does not hit. The engine will move around a little even on a hard mount. If the engine is on a vibration damping mount....then I normally run about a 2mm gap and sometimes more.

Troy Newman
Team YS