All insulin's used in the UK are U100 the same strength, you can import a U500 insulin from America but this has to be done under special licence for the individual patient.. I'm sure U100 is now world wide...
Percentage is really only a guide line, in common most people will fall into the 40-50% range somewhere, teenager can go as high as 60%... In the main when the health proffesionas work children''s out, they take several factors into consideration.. Previous TDD, current A1c's and weight of child then number crunch..
Another factor that plays apart in the percentage game, is activity levels, it's likely a more active person would have a lower percentage..
I would have a word with the diabetic nurse, she would be better able to explain it all