Fix1: Any time you set a target number and have modifiers over 21 something special happens. You subtract 7 from the target number and that becomes a negative success versus the roll. So a tart number of 22 becomes 15s1. This continues to happen for higher target numbers. A target number of 32 does not end up at 25s1 but rather any time you exceed 21 you subtract again. Making the target number 17s2.
Fix2: Hard cover is going to force a negative against the to hit roll. So if someone is ducking behind a wall and peaking out and firing you are going to need to hit both smaller target and deal with cover that subtracts from the two hit roll. This will be set as negative one success for any type of hard cover. a tree or a building all are the same. Something like a murder hold a castle could be two but very little else.
Fix3: Firing several range increments may start create a negative success value for very long ranges. Say shooting five or more range increments.
Fix4: The players and game master have use of success tokens these need to be more free flowing for the Game Masters. Name enemies may need to have their own success stone pools.
Potential Fix: look at range and scale.