To the OP you chose well. Especially if you live for off-piste.
I got a pair of 196 Lhasa Pow primarily as a powder and day after ski. The Lhasa were quickly my go to ski and by the end of the season I realized I had a 1 ski quiver with a bunch of rock skis / backups. The traditional camber & sidecut with rocker really worked well for me. The Lhasa skis groomer and hard snow surprisingly well. Enough so, really do not think about using my other skis.
Time to simplify, once we get some decent coverage I only plan on skiing my Lhasa. (If we get super hard snow I might break out my stocklis)
Anyways, take the Lhasa Pow out in more than just new snow. I think you will be happy.
For anyone else making the 186 vs 191 decision(or 196/191). I think there are strong arguments for going longer or shorter. The Lhasa is very maneuverable for its size (rockered, pintailed and light weight). So going a little long should be OK. The Lhasa tip has a great float and the pintail helps with the effect. So you should not be too worried about going short in powder. So only if you are really concerned about float or stability at high speed over rough snow, would I say no to the shorter length. If you like short turns go short. If you like to going fast go long.
That said, I would buy a 203 or 205 Lhasa Pow if they made it. That would be a fun deep snow fast ski.
ps - Make sure to have the shop measure the mounting point. (Don't trust the line on the skis...)