Ski size for Armada Thalls

I am 5'9" 165. I have been skiing the fatypus g butters for the last few years which are 178. They were my first real park ski. I felt really comfortable on them. I wanted to try a softer ski for park and I had an opportunity to buy the 176 Thalls from last year for $100 new. Had to get them. I got to do a few runs on them yesterday after work and had a bunch of fun, but definitely noticed the difference in length. I feel like this should be the right length for my size and wonder why 2 cm feels like so much. Will it just take some getting used to? Also as a side note, how should I detune them before hitting rails?