Success and damage:
I find that my players don't want to bother with reckless stance because they often need just 3 successes and any extra successes are wasted. For that reason I have decided that any successes above 3 give extra damage. I allow players to pick multiple damage bonuses from successes. 4-5 successes would give the player +3 AND +1 damage. 6 successes would give 2x+3 damage on the card. That way it's more rewarding getting more successes. I use the same for multiple critical wounds etc. I just allow players (and monsters) to use all the successes, boons, and comets to gain multiple effects. The same is true with banes and chaos stars of course. This gives more variety instead of damage just being either 9 or 11 for instance and no other result possible. Chaos stars also cancel a success as well as giving the extra effect.
Assisting in combat:
I do not allow assisting in combat to give other players an extra fortune die. As it is I find that with only one purple die under normal circumstances it's hard enough to fail altogether even for freshly created combat characters. Instead I allow another kind of defensive assist. If two players are engaged with the same npc one of them can assist the other allowing him to perform a parry or block for an attack against that player. This could lead to two blocks against one attack or even two blocks and two parries. The assisting player uses his free maneuver for this assist and he uses his active defence card(s) as well.
Fixing the high hit percentage while maintaining variety:
1. You subtract 1 success for every point your enemy has in melee/archery/athletics/whateverskilltheGMthinksfits
2. Defence adds black dice as normal
3. Default difficulty for an attack is average (2d).
4. You need at least one hammer to use a sigmars comet as a success.