Can you set the wizard in the Expert meter to recommend by half units instead of only whole units? Half unit pens are easily available. Pumps of course can dose to 0.05u accuracy. So there is less of the "free carbs" due to a rounding error on the wizard.
Just as my basal rate changes throughout the day, my I:C ratio varies according to the time of day. At breakfast it's currently 1:13, whereas at 10pm it's 1:10, irrespective of what I'm eating. These ratios have all changed as my weight has shifted, upped my activity, etc., etc.
On pump. Never worry about eating snacks.. Always bolus for what I eat. Like previous poster mentioned.... Corrections may cause stacking (more so on mdi) but then on the accucheck pump if you have your offset and acting time set up correctly it does work on the times etc you have set up. So even on corrections I never worry as the accuchek pump is prettydamn good ifset up correctly.