Unisystem is a weak system on many fronts. It is math heavy, it fails at scaling to more powerful game settings (like Armageddon or Witchcraft) and it has no fumble system.
While fixing the scaling issues are outside my desire right now, and the math issue is just an endemic failure of the system, the “fumble” issue can be fixed.
I decided that the number under 9 can be used like that over 9. 8-7 are 0 Fail Level, 6-5 are -1, 4-3 are -2, and etc. These FLs are added to the opponents SLs if applicable, or used to decide how bad everything got. In a driving failure they are used like SLs for damage to the vehicle.
It is not a perfect system, but it has worked fairly well for me.