I'm eight years post diagnosis and I take a dozen of the Sinemet 25/100 a day.
If your getting relief from symptoms with minimial on/off cycles on three a day, then your doing good and have a lot of room to increase the dosage.
Three was my starting dosage in 2015

MD Appt 6/1. Sx worse in am. Thinking about slow release meds

Not sure what the highest dosage is I take 8 a day