A lot of T1 diabetics will find that they are least sensitive to insulin first thing in the morning and more sensitive as the day goes on. My ratio is technically 1:12, but I just use 1:10 as on MDI, there is no way to discriminate between 1:12 and 1:10 unless you eat >50g in one go. Which reminds me, I should really get a half unit pen for that reason...
Anyway, I just use 1:10 throughout the whole day and I seem to be sound. I do go to about 1:20 for meals following fairly strenuous exercise, as the exercise makes me very sensitive to insulin but only for 4 hours or so after the activity.