My TDD is currently 54 units. My usual plan is to eat no more than 35-40 carbs per meal. This leads to a bolus of 2.5 -4.5 units depending on many factors. Of course sometimes I go off the deep end (like thanksgiving or when I order my favorite pizza). A few weeks ago my family got a 3 meat pizza and I could not resist a third slice. 3 slices = 96 g carbs. I dosed something like 8.7 units with 6.8 normally (upfront) and 1.9 units squared over 1.5 hours. I got lucky with the bolus and the highest I tested was 141 about 2 hours PP.
I am not sure if insulin leekage/seeping is my concern for big boluses. I have two larger concerns. A huge carb load may digest differently than my normal meals (slower, faster or all at the same time). This is a variable I cannot always predict. The other issue is when the insulin is absorbed. I believe Bernstein is against large injections because they can pool under the skin. If there is a "big" pool of insulin under the skin, than is it all absorbed at once or can only the outside be absorbed and the middle is absorbed slower? Another variable that could certainly be at play for large boluses.
Occasionaly I have noted leakage issues, but I attribute this more to equipment problems like a bent cannula.