I had this problem with my DD2 who was-shall we say- more "generously thighed" than my DD1 !!! I found that motherease onesize and my smaller pockets just would not do up with DD2.
We moved over to a combination of Toddle-Ease (these are extra large Motherease Sandies in style, popper so child can't undo them, and can hold a baby elephant, esp when extra boosted) and Totsbots size 3s, with either a motherease XL airflow wrap or a size 3 Totsbots fleece wrap over the top.
This got us through the six months or so before she was ready to potty train: i found as a toddler she needed less nappies (6-8 in total) but the downside is there are very few about secondhand as not many mamas use the larger sizes, and those that do tend to hang on to them!
Good luck, I do think fitteds are the way forward for power wees as they just have better capacity.