Well most people who didn't play like a year ago don't really know how the Yuki clan was. Berlin designed it to be the weakest defensive clan but have the best attack in the game. In the end he probably succeeded but the way he made Yuki required it to have to bind to win with ice prison.
Reformist probably didn't like that so he nerfed ice prison to the point where it rarely hits, the problem with that is the clan has one fast projectile (senbon wave) and will not hit much of anything else without ice prison. As a result, Yukis are the worst clan in NNG. So instead of simply buffing ice prison's size again I suggest doing something more productive.
Make iceberg breaker move faster, but mainly fire faster. It fires very slowly and stops your movement for a second when you use it, which makes landing it hard if you are a clan that's supposed to be on the move. Make it activate as fast as other projectiles, e.g. Dragon Flames.
Increase the size of ice prison to 5x5, I think that's what it used to be. But as a penalty, while in ice prison enemies take 50% less damage.
Make the final skill, ice dome do something productive like senjus does. For example, let it buff crystal ice mirrors damage while its active, ice mirrors is kind of weak anyway so make it do 50% more damage while in ice dome.
If anyone else has any ideas feel free to comment, just need to get the word out there that Yuki is broken and needs a buff badly.