you need to match the master cylinder size with the braking system front and back, I did on the 100E back in the day as I went from drums all round to ap 4pots on the front and 9 inch drums on the back lol
basically bigger pistons (in the calipers) need more fluid to fill the cylinders so you need to push more in there with a bigger master cylinder not the same amount at a higher pressure, if you get my drift

steve