XCOM EU Will vs Psi Attack forumla

[themaster408]

I'm running a homebrew XCom tabletop game (think D&D without any role playing). I've tried to make it nearly exactly the same as XCom with a few minor tweaks. I've found formulas to hit based on weapons, aim, defense. I've found formulas on research speed, how expensive something is based on engineer and workshop count, but I can't find anything about Will.

All I find is "Will helps defend against panic and psi attacks". Ok, what is the exact formula? I see Long War shows a percentage and figured this would be a good place to get a direct answer.

http://ufopaedia.org/index.php?title=Morale This helped me with figuring out panic, but seems it's based on Bravery

http://ufopaedia.org/index.php?title=Bravery Talks about Bravery

Neither of these even mention Will. There's links in the wikis above that talk about Psi attacks lowering Bravery, but still no mention of how Will helps.

Please post an actual formula (or a close approximation) if you can. Even simply "Will of 10 gives +10% defense to panic. So if you have 40 moral, 20% chance to panic, but if you have 40 moral and 10 Will, then it's 10% chance to panic).

Thank you.