Sorry that I came across as a butt-head...even though I am one. I do not like to sight my guns in that high (3"), especially that ones that shoot that flat. I like them to be just like the chart (but w/maybe a 225-250zero) 7-8" low at 300 and 18 or so at 400.
You need a rangefinder. But, at 300, I like to put the cross-hairs on the back, and If I shoot 400, I take my time, get a real-good positon and hold about half a body height above the back.
Now, Jack O'Conner recommeded a zero like that. But, it gives you a bullet that is about 6" away from your line of sight. Based on the Remington recommendations ( and also the Winchester and Federal recommendations) your bullet is dead on to 250 yards w/no corrections needed and depending on where you like to hold, no corrections needed to 300.
I also note that I didn't really answer your question...as you asked about a zero that was 3" high at 100...I don't know the answer for that zero.