I would imagine that the only answer for width of bucket would be as snug as possible without hindering rotation.
What benefit could be gained from flopping all over the place?
Knees high or low will always be a personal thing with wildly varying answers.
I think that generally, height of the seat relative to the foot well always be a compromise in stability, so differing skill level paddlers will want what ever suits their particular preference.
Some find no issue with high feet/ low bum, some hate it.
I think most will agree that general fit guidelines is best satisfied by getting in the ski and see if you like it.
If you do, you do, If you don't, you don't.
It really is as simple as that.
Now lets get on with the more important issue of arguing whose backside the seat should be moulded from.
Follow the path of the independent thinker. Expose your ideas to the dangers of controversy. Speak your mind and fear less the label of 'crackpot' than the stigma of conformity. And on issues that are important to you, stand up and be counted at any cost.--- Thomas J. Watson