While that is annoying, I would argue this isn't an issue with the units, but just a fact about how probability works.
Setting aside micromorts, you can't say a 50% chance of death + a 50% chance of death = 100% chance of death, either.
Setting aside micromorts, you can't say a 50% chance of death + a 50% chance of death = 100% chance of death, either.
(assuming your aim is good & lethality on hit is 100%)
But when some unit looks like a meter or gram (especially using the micro- prefix here), it should behave accordingly.