I suggest just remove the second hit, and its damage is added to the first strike.
This burst and defence boost, rather than damage.
For example:
Before:
Evade and stab your foe in the back twice. First strike removes 1 boon.
Damage: 252
Second strike damage: 504
Range: 130
After:
Flanking Strike. 4 ini
Evade and stab your foe. Strike Removes 1 boon.
Damage: 756
Range: 130