Never had one but a question about colonoscopy preps?

Because I enjoy avoiding housework I was thinking about colonoscopy preps. Does it not sound fairly logical that a 350 lb man or woman would need more of the chalky drink than, say, a 98 lb person? And, if so, shouldn’t the 98 pounder therefore get a break and get mini size drinks? Or a whole lot less? It seems that all of us are expected to drink as much as an elephant when some of us could get away with the shitzu amount? If I ever had it done I would cheat. I would drink half of the stuff.