It's possible there are different alternatives that have different dosages. If you really wanted to find out though, you could always ask your doctor. Dispense as written can be used because the doctor gets kickbacks, but there are frequently more innocent reasons for it. Perhaps the adhesive isn't as effective, but ultimately there are any number of things that can differentiate generics from brand names or other generics. Pills tend to be more similar, but even then there can be differences despite technically being the same drug.
It's possible there are different alternatives that have different dosages. If you really wanted to find out though, you could always ask your doctor. Dispense as written can be used because the doctor gets kickbacks, but there are frequently more innocent reasons for it. Perhaps the adhesive isn't as effective, but ultimately there are any number of things that can differentiate generics from brand names or other generics. Pills tend to be more similar, but even then there can be differences despite technically being the same drug.