Fentanyl is a very, very potent pain medication. It is dosed in micrograms instead of milligrams because of its potency. It’s not the dosage that matters it is the effectiveness of it for you. Thankfully, fentanyl seems to be consistent in its pain relief long term.
As far as drop foot goes,I have it bilaterally in both feet and have not found it painful, so I am a bit surprised you do, unless you are referring to nerve pain from the failed radio frequency ablation? Have you had ongoing nerve pain since the ablation? There are different meds that work really well to treat nerve pain you may want to discuss with your pain management doctor. He may consider adding one to try to ease the nerve pain, rather than worry about doing anything to the current fentanyl dose.