@ttyymmnn Everybody'd situation is different but head droop was what triggered our inquiry into working on dad's dosage. That got me talking to my cousin and learning that you need to really work with the dosage over the progression of the disease. We increased dosage and it helped. Simply put, dad was taking a lot less medication than what he needed.
Droop is what the medication is intended to fix. I suggest talking to his doctor and try different dosage levels and also a mix of slow acting and fast acting.
Unfortunately Dad's first doctor was a nurse practitioner who had little experience with Carbidopa. She gave dad a standard "learner's" dosage and never followed up. We got my dad into my cousin's doctor who was an Parkinson's expert and he encouraged us to find what worked for dad.
Carbidopa is really good stuff, but it takes active management to get the most benefit. I think most doctors prescribe 30% the needed dosage because they don't have the time to fine tune it. In my assessment 30% gives 25% (or less) the benefit with no risk or needed follow-up.
I wouldn't be ok with 25% the benefit if that means drooping for the afternoon. You might as well make the most of it, so if the doctor is not helping you, go find another that will work more closely.
By the way, drooping is not the only issue. Decreased swallowing gives you aspirational pneumonia which is what kills many with Parkinson's. So one other thing is I would be actively be looking for choking issues. If he is coughing while and after eating, you may need to look at grinding his food.