Are your inserts microfibre? If so, they are great to soak up wee really fast but when full, it compresses out really bad - like squeezing a wet sponge.
You could try bamboo inserts such as P'tis Dessous or Greenkids which are quite slim fitting with an Easy Peasy hemp booster underneath the bamboo. I had to stop using m/f inserts when DS2 was 1 then switched to bamboo & hemp which is the best pocket combo.
The wicking could just be due to the wee being squeezed out of the m/f insert - you may see a change if you try other inserts. Hope that helps