As said, MOA isn't exactly 1" at 100 yards and as such, as the distances increase, the difference between the two becomes apparent.
If your scope really is 1/8" per click at 100 yards that adjustment will change proportionality with changes in range. At 200 yards it will move impact by 1/4", 400 yards will be 1/2", 50 yards will be 1/16" and so on. So for 31" at 400 yards, you need 62 clicks.
Those numbers of elevation (both MOA and inches) are from a given zero, I'm guessing 100 yards but don't know. What you do is zero the rifle at whatever the specified distance is on the ballistics chart and then from there you adjust whatever the number of clicks would be. So if it says to zero at 100 yards, then if you go to 200 yards and you need say 10 clicks of elevation and then at 300 you need 25 clicks, both would be relative to the 100 yard zero. So if you zero at 100, add 10 clicks to get to 200, then decide to move to 300, you would only add an additional 15 clicks to give you a total of 25 clicks from your 100 yard zero. (These values are made up for simplicity of the example, but would just be replaced by whatever your ballistics chart states).