The amount of times lae'zel misses is staggering. I had fights where her hit chance was consistently around 90% and she didn't hit once. So, what I am saying is that the percent chance seems to not matter too much as such. Characters with darkvision, such as Astarion, seem to have less misses when having the same hit chance. So, like others mentioned, there are factors affecting your hit chance that are not expressed in the numbers and are not very clear.
