Utilt typically hits from a purely vertical angle to an angle of 65 degrees. It depends on where you are when his second foot connects IIRC - remember that it's his first foot that has the two hitboxes.
This will likely be a multi-day project, since there will be a load of trial and error trying to get a kill range within 5% - 10%, and the fact that there are stage boundaries to consider (I think we can go for the average boundary and the two extremes: the top platforms of Green Greens, and the bottom platform of Jungle Japes), so if you ever want to quit at any time, feel free to do so.
This will likely be a multi-day project, since there will be a load of trial and error trying to get a kill range within 5% - 10%, and the fact that there are stage boundaries to consider (I think we can go for the average boundary and the two extremes: the top platforms of Green Greens, and the bottom platform of Jungle Japes), so if you ever want to quit at any time, feel free to do so.