I believe the "nerf" here was to reduce the distance chicken can run *when* they decide to run. Your original question was why they are *not* running. Because, I did find that chicken was able to run too far, which would cause you the trouble of having to waste a lot of APs to catch up to them when you get your turn - and that is just dumb. So I'd say that, I believe the "nerf" has nothing to do with how likely they will stay still or will run when they are in chicken form. The nerf means it will be easier for you to catch up to the chicken when they run away.
Last edited by Try2Handing; 11/10/17 09:48 PM.