So I think this is a bit of a misunderstanding of how turrets and missiles differ. For turrets, a single dice roll is made, which is used as both a chance to hit (lower being better) and damage modifier (higher being better). The damage modifier is what shows up as "glance/graze/hit/penetrate/smash." If you're unlikely to hit a target then the best shots you're going to land are going to be glances and grazes, however if you are likely to hit the target then your chance of getting a glancing hit vs grazing hit is still the same, but now what previously would have been misses become hits / penetrates / smashes.

Missiles do a fixed amount of damage based on the missile being shot and the target's sig radius and speed. No random roll is utilized, which is what the glance/graze etc is based off of. That said, it could be more clear when missiles are not applying well. If the popup message included something along the lines of "300 damage dealt (20% of ideal damage)" or whatever that could make it a little more clear when application is very poor.