How it works now:
Skill gets multiplied by elven gear (if any) first, then by a certain factor if it's a ranged round.
Current round effective skill level gets added as defensive dexterity.
Physical weapon DX-based chance to hit is calculated depending on attacker offensive DX against defender defensive DX.
It is then CAPPED to 160, 180 or 200, depending on weapon type.
Weapon PTH gets added to that capped value.
Current round effective skill level also gets translated to a certain "minus chance to hit" which is put on top of that previous attack chance to hit value.
End effect ? DX-based chance to hit drops, weapon plus drops but it also affects DX-based chance to hit in case the evasion is higher than the weapon pluses. It's at best a double-dip, or you could even consider it a triple-dip.
HOW IT SHOULD WORK - DIFFERENCES
Only half of the evasion skill levels get added to defensive DX.
The other half of the evasion skill levels get translated to a "minus chance to hit".
DX-based chance to hit is calculated and is upper-capped at 200/180/160/whatever.
Weapon plus (and any leadership or other PTH bonuses) gets calculated and has the evasion-based penality subtracted from it. If it goes below zero, it is bottom capped to 0.
The two previous capped values get added together for the actual chance to hit.
End effect ? Evasion is still good at reducing DX-based chance to hit, it still is good for countering USD plus to-hit weapons, but it no longer double/triple dips.