Just thought I'd post an update on this. Had to give up on WNNN altogether because of the leg gape - its not an absorbancy issue its fit with these for us. He's just too skinny!
Boosting Lollipops at the hips by putting an extra bamboo booster round the outside solved the other issues. Also I bought a LLS nappy preloved whcih was amazing and a perfect fit! That under wool was always reliable.
He's become less of a heavy wetter now he's 7 months and weaning's well under way though and he has fewer night feeds so we're back to being able to use bambooty nappies at night too.