Hey, thanks for making this! It seems quite close to being accurate, but I think it may be
slightly off (very close, though). It's a very great resource, but I think it may be able to be improved slightly. Sorry if this comes across as pedantic, but I've done a lot of level range testing and there is always confusion about 10 + 10% vs. 10 + 15%.
A couple things -
1. I don't believe the co-op range was ever 10 + 15%, not even for sunbros, so I would consider removing mention of that. I did level range testing in 1.05, 1.06, and 1.07. I'm certain that the belief in the 10 + 15% formula comes from a mistake where players tried calculating from the host's level. You can't do this, as the range is calculated from the phantom's perspective.
Here's an example:
One player who believed in the 10 + 15% formula (the commonly-referenced steam forum DaS network guide, which has a lot of other good info about co-op), cited testing where a level 65 host could summon a level 83 phantom, but not a level 84 phantom. If the range is 10 + 10%, they must have wondered -
how do you summon a level 83 player when 65 + 16.5 = 81.5?. They thought that the 10 + 10% formula couldn't explain this "larger" range they were finding, so they tried a 15% formula which they thought gave them a correct answer (but it actually didn't..., although it appeared to be closer).
However, they failed to try calculating 10 + 10% from the phantoms range, where the calculation is actually made (I've tested this). 83 - 10 + 10%, or 83 - 18.3 = 64.7, which should round up to 65. They thought they needed a bigger formula to explain why a level 65 could summon a level 83, but didn't consider that it's the other way around - the level 65 player is in range of the level 83 player.
In a sense, level matching is a one-way process where summon signs find the hosts. The signs are only sent to a host if the host is in range of the phantom. The phantom doesn't have to be in range of the host. Same goes for invasions. The math is done by the phantoms.
That being said - this DOES mean that a host and a phantom at the same levels have a slightly different level range. I wrote an explanation here that explains it in detail, with an example level ranges table showing the different ranges for hosts and phantoms:
http://darksouls.wikidot.com/co-op
2. The calculator currently states that a level 100 player can be paired with levels 81 - 121. This is quite close, but like I said there should be slightly different ranges for hosts and phantoms. The phantoms should be able to paired with hosts between the levels of 80 - 120. A level 100 host should be able to be paired with phantoms between the levels of 82 - 122.
Because finding out the range from the host's perspective is more work (requires calculating 10 + 10% from two different levels, in this case 82 and 122), I would suggest fine-tuning the calculator to only calculate from the phantom's perspective.
In this case, it
should come out to levels 80 and 120 exactly. I'm not sure how 81 and 121 can be reached with rounding, because 10 +/- (10 + 10%) at level 100 is +/- 20 exactly, which is where I see a small error with the calculator currently.
I might also reword the field that says "Soul Lvl" to "Soul Lvl of Phantom", and "Min." and "Max." to "Min. Lvl of Host" and "Max. Lvl of Host". Or a note beneath it that clarifies that you're calculating from the phantom. Without it, players might not know which perspective they're calculating from.
- - - -
If not, this is close enough to still be a very handy resource, and I highly appreciate it.
I just wanted to point out that 15% never worked and that phantoms and hosts have different ranges.
by 
)
