For the most part accuracy calculator agrees with the ATA calculation above, it doesn't seem like the author knew the formula though so what he used was some really odd formulas which seems to approximate the ones I posted in the previous post. Also accuracy computation is just (ATA - EVP/5) = accuracy in %s.
If you multiply out the table you should see accuracy-wise N3 > N2 > H3 > N1 > H2 > S3 > H1 > S2 > S1, where alphabet means whether the attack is normal/heavy/special and the number is whether the attack is the first, second, or third attack.
This gives some insights: for example, if NSS hits then HSS hits for sure, since H1 > S2. For low ata non-sacrificial weapons such as hitless TJS, second H is the toughest part to hit in NHH, since H3 > N1 > H2. For sacrificial weapons on certain hunters without insane ATA or low EVP enemies, in general NHS is about the best you can get since S2 is quite a bit less accurate than S3.