Perhaps related to my recent right hemicolectomy, I cannot take more than about 4 or 5 grams of ascorbate before diarrhea arrives, but I cannot find specific/solid evidence that supports (either for or against) dividing up the dose into, say, 3 grams three times a day to avoid diarrhea but retain the CAD protective/reversal effect from Linus Pauling's recommendation.
Because of the short half life of most absorbed ascorbate, I feel that divided dose intake should be the same or even better than one dose per day of at least 9 grams (is this your minimum?), since for any specific dose the arrival of diarrhea means that there is an osmotic effect of the excess ascorbate (my guess), meaning that it is lost/not absorbed by the system.
From Hickey/Roberts Ascorbate: The Science of Vitamin C we learn that for people, without an extraordinary need, perhaps 250 mg every 3 hours keeps blood levels optimal. (Due to absorption issues and loss in the gut, we recommend 500 mg every 3 to 4 hours as a general tonic)
With 16 waking hours, that would mean around 5 doses or 2500 mg daily.
Some people have a higher metabolic need apparently.
I take say 20,000 daily, and with 5 doses that would be 4,000 mg each dose (rather than 500 mg)
For convenience I follow Pauling and have taken 9,000 mg at one time (twice daily) for years. (This is probably not as efficient as taking lower dosages more frequently, i.e. more is lost out the urine.)
As you say there might be several reasons why your bowel tolerance has dropped, and one thing to think about is using liposomal, even 1 or 2 grams daily, in case the problem is absorption. True-liposomes are almost 100% absorbed into the blood and seem to much better absorbed into cells.