i have experienced that "trench" too, not fun.
food has always affected my absorption but not until recently has just taking 50 or 100mg not helped and gotten me back to tolerable. could be gastric emptying but i have fasted and still experienced this reduced effectiveness, still could be gastric emptying, can't wait for inhaleable l-dopa, quick way to diagnose the digestive system as a factor.
or even those apomorphine oral strips when they come out, hopefully a quick fix to get over a hump?

certainly curious what this might be if not gastric emptying, and i'm not really off physically but mentally, so something else might be going on.

in the "parkinson's disease treatment book", to paraphrase:
"if you are doing well 1hr after your dose, 2 hrs if taking CR, then you have the correct dose.. you can raise the dose by 1/4 to 1/2 tab increments until you find the dose that works if CR, increase by 1/2 tab.. once you have figure the dose then you can address how often. rarely sees any benefit from higher than 300mg (!!) except taken close to meals. ceiling dose of 25/100CR tab is 4 tablets!!

when you find the dose, calculate how long it takes for the dose to kick in and how long it lasts, then reduce the interval between doses so the effects slightly overlap..

better to shorten time between doses than increase the dose size.

the book goes into taking 1/2 more tablet before meals, drinking a lot of water with each dose, sugar can help but doesn't recommend. and says mysteriously sometimes advanced pd'ers just have a bad day.