Parashooter, thank you thank you thank you. This is what I was looking for. And yes I am using factory loaded ammo. I have just under 2000 rounds so I don't plan on using any other loads any time soon.
I fully understand that I should probably just leave the front sight alone and just use the backsight for this by counting and recording clicks rather than using the graduation marks on the sight. This is really what I'd rather do anyway but my reasoning of establishing 200 zero at the 200 mark on the sight first using the front sight is to to give me an easily recognizable starting point. Like on my AR15, my 6/3 is zeroed at 25/300yrs. I can do -6 clicks from 6/3 for 100 yrds or -4 clicks from 6/3 for 50/200yrds. On the Enfield I am just looking for a good logical easy to remember starting point like 200 = 200 so that 1) I am not having to remember odd ball numbers like the half way point between the 200 and 300 yard mark on the sight really equals 50 yards, and 2) I won't have to count an absurd amount of clicks from bottoming out or from other starting point on the sight. The settings on the AR work well because I can always just quickly return to the 6/3 mark and go from there. Now I try to imagine if there was no 6/3 mark and the dial was just blank. What setting was I on again? Let me count down clicks to bottom out and then count clicks back up again to where I need to be. Woops I didn't hear that one, did it click or not, should I count that as a click? Start over... The entire point of my original question was this: If I establish my zero of 200yards at the 200 mark on the sight will I be able to use those remaining -3 clicks that I have available (bottoming out the sight) to put me right on at 100 yards? This is why I originally asked about the drop from 100yrd to 200yrds. In other words, if I am zeroed for 200 yards (with the sight set to 200 yards) and I am shooting at target 100 yards away then I should be about 2.5 high right? Then I just lower to the sight -3 clicks to bottom out and...

I've always used a center hold and zero for these types of rifles because it doesn't bring the size of the target into the equation as an additional variable that has to be corrected. If were to use a 6:00 hold then the POI changes with the size the target if I want to hit the center. In other words if were to hold at 6:00 on a 10 inch circle at 100 yards and I am hitting the center, then when I move to a 5 inch circle at the same range with out changing anything else then I am no longer hitting the center when I hold at 6:00. At this point if I want to hit the center then I have to either correct for it with the sights or try correct for it by guessing where to hold in the open space below the circle.