it is due to pressure drop through the solenoids and plates. a nos big shot noid might only drop pressure from 900 to 400 but a similar nx might drop pressure to 350psi
now with a diff amount of pressure at the jet will change the amount of spray.
im shure its not a lot but there is deff a diff in jetting. a 150 nos shot uses more fuel jet than a similar nx kit for the same power level.
but a lot of people have mixed and matched and made it work. evan more have holes in the side of the block and pistons with fried carbs because they got it wrong. i would say call nx to see what their jetting is then go to holley.com techlibrary to get the nos jetting and go off of that.
ive ran power levels up to 300 and never evan burnt 1 spark plug. but ive always stuck with one mfg and one kit well two kits. dual cheater and big shot.
but if you havent ever sprayed before and keeping it below 150 you should be able to tune off of the plug . just pull more timing and use a little larger fuel jet and sneak up on it. i used a digital 6 to pull my timing. motor at 36deg locked out. box pulling out 4 deg on 125, 6 deg on 150 and 8 deg for 225 with 9.9 deg at 250 plus.
i always ran below 225 shot with a ngk r5671a-8 then 250 and up r5671a-9.
deff run a colder plug evan though they say stock heat range at 150. its cheap ins.
i hope that helps at all