Anybody know the leeching formula for EXP at LHC/LKC or SH?

The exp is actually cut into 60 / 40 portions for damaged-based sharing and level-based sharing, respectively. I.e. 60% of the EXP goes to people who kill actively, 40% is distributed among party leechers. We call it the 80-20 formula because in a party of 2, the killer gets roughly 80% of the EXP (60% + 40%/2) and the leecher gets roughly 20%.

E.g. A party of 2 (with 1 leecher) each gets 20% of the EXP from leeching.

For the case study, here's the distribution calculation:

- Kill EXP: 60% * 100,000 = 60,000 EXP go to the lvl 160 killer.
- Leech EXP: 40% * 100,000 = 40,000 EXP go to everyone (including the lvl 160 killer).
- This 40,000 leech exp is then distributed with appropriate weights (levels) to the party. I believe the formula is something like EXP leech = TotalEXP * (charLevel/partyTotalLevel), in other words:

Now, party play effect comes into the picture by kicking up the leech EXP (from 40%) by partyNumber*50%. In other words, the leech percentage is now 340% for a party of 6. I don't know exactly how it behaves, but I believe it just boosts the leech exp from 40,000 (out of the total of 100,000) to 340,000. My bad, forgot that it only adds 50% per member other than yourself. So together with regular party bonus (5% per member), the total leech EXP gets boosted to 280%. I don't know if it is additive or multiplicative, but I'll assume additive since multiplicative wouldn't yield the kind of EXP I see at LHC. Overestimated, it seems multiplicative like Sapta suggested.

This 280% is added on top of the original 40%, yielding 320% of the monster's exp as Leech EXP. In other words, 320,000 is distributed among party members by level, this table is yielded (HS optional):

 party bonus being additive, seems like a gross overestimation

P.S. Here's the spreadsheet.