It's been years since my hth spec, but IIRC evasion is just a group feint (with maybe a higher chance of working than regular feint). In actual gameplay it's pretty much a useless (and redundant) skill only amounting to wasted practices. So here's an idea for a revamp of evasion (in the form of a helpfile, with more details below):

EVASION

syntax: evasion

Hand-to-hand students may in combat choose to focus on defensive
techniques, thus avoiding or deflecting blows aimed at them more
efficiently. However, while concentrating on keeping themselves out
of their opponent's reach they also have fewer chances for strikes of
their own. FEINTing incoming attacks is also more effective while
evading blows.

Evasive fighting may be activated and cancelled during combat as
the player sees fit, but at the latest it ends when combat stops.
--

Effects of EVASION 'ON':

1) improved chance for DODGE and PARRY/IRONHANDS
2) (large) penalties to THIRD and FOURTH ATTACK
3) improved chance of success on FEINT skill (which might also occasionally feint everyone fighting you)

Activating/cancelling EVASION would take 1 rnd of combat, e.g.:

"You start focusing on defensive hand-to-hand techniques."
"You resume a less defensive fighting stance."

Alternatively you could make it a toggle (evasion on/off), so it'd always be 'on' or 'off' without having to enter combat first (cancelled when wielding anything). Another idea is to have it work similar to caltraps, so that if either party flees evasion stays 'on' till next tick (thus often no need to reset it if re-engaging right away).

I don't really have an opinion whether evasion should work cumulatively with imperial defense/offense (offense mitigating the reduction of attacks), but if not I guess imperial off/def setting would override evasion. On the other hand it would be cumulative with legacies that boost defenses (such as WARD or DANCE).

Finally, COUNTERPUNCH edge would switch to trigger on FEINT.