both carbidopa and l-dopa should be out of your blood in 4-5 hrs. keep in mind that in the early stages of pd where you still have some functioning neurons in the substantia nigra, those cells will accumulate l-dopa so you don't have wearing off. but there are mechanisms that tightly regulate l-dopa concentrations in the brain. getting too technical here.

how long have you been taking 100mg of C/L? can i ask what the NDC is on the RX label? this is a number with the format like 0093-0293-05.

what supplements are you taking within an hour of taking the C/L? I've noticed taking a multi-vitamin even an hr. before can negate the affect of my C/L, possiby due to B-6.

In the book "THE PARKINSON'S DISEASE TREATMENT BOOK" Dr Ahlskog starts patients with 25/100 C/L 3 times a day.. Some people start with 50mg three times a day but most people can tolerate 100mg. the exception is for nausea. it may take a few weeks to find the right dose.
week 1 - (3) 100C/L stop here if works OK otherwise
week 2 (3) 150c/l
keeping increasing by 50mg up to 350mg 3 times a day - wow!

i guess the point here is this neuro has people start with 300mg/day or if the get nausea 150mg/day. then increases the dosage weekly until the best dose is found. my advice is talk to your neuro, he must have a reason for giving you such a low dose for such a long time. the goal is to get the best symptom relief so you can improve the quality of your life? that said, i noticed a beneficial affect from my first dose of 50mg C/L 9 years ago, i have no tremor. tremor can be drug resistant.

i'm not a doctor so take what i say with caution and talk to your neuro.