Hello ,
Maybe i`m mistaking the terms , but so far i have figured out that.
Taking your example for 43% and your estimate of 40mil shares on your pool .
43% from 40mil = ~17mil shares . On NOMP if there is 20mil shares on the found block then yes , they will be paid more (as normal) . But if miners leave on the 17th mil share and until block there is another 50 million shares the first 17mil will cost less than original (which is normal too since the block will be split between 67mil shares in the second example and between 20mil shares on the first example) .
PPLNS are for big pools and such . So far we are struggling with our first block
Regards