Help me with my strip washing pleease

I'm having issues with Findlay drenching all his night nappies (even his Puddlekins custom which was made to have more absorbancy in it than he actually wees so no idea how he is soaking it) so I am going to give them all a good strip before he goes into hospital in a few weeks so they are as absorbant as possible.

I usually strip by doing a cold rinse, a 60C intensive, super rinse cycle with full amount of Ariel Bio detergent (+ Lakeland dolly balls to bash the nappies around more) and then approx 3 x 30C full wash cycles (with no detergent) and a couple of hour long rinses which is usually plenty to make sure there are no bubbles.

I did this not long ago so I wouldn't have thought the nappies would have detergent build up and he was still soaking everything even immediately after the strip wash.

When doing my standard nappy loads I do an hour long cold rinse, intensive super rinse cycle with about 40ml of powder and then a long 30C wash with no powder to give them a good rinse out and if I see any remaining bubbles I'll rinse them again.

Is there anything else I can do when I strip them? (I use a mix of fitteds, pockets and some AIOs) Would trying a different detergent when I strip them make any difference?

Also how many nappies do you put in at a time when you do a strip wash?