Zeroing at 100 is more reliable with elevation changes, you wont see your zero change due to elevation at that range. It's the rest of your dope at longer range that will change. Plug it in for your parameters, but depending on what you need and your conditions it may not matter enough to actually matter.
For what it's worth, I live at a DA of 1300' (today), and I compared it to a DA of 5000' using my dope for my .270win. My solution only changed enough to register a .1 change beginning at 375 yards, and it's still only a click different out past 500. My short-barreled 6.5cm changed .1mil beginning at 350, but it was within .1mil out to 500 as well due to rounding to the nearest .1mil. So the effect isnt so significant depending on the maximum range you are counting on being able to shoot. In other words, going from roughly 1000' to 5000', on both of my rifles, if I was zeroed at 250 yards my scope doesnt have enough resolution to adjust the difference. It's near the end of my effective range I'd be more worried about (.1mil @ 400 or 500 on top of my wobble, ranging error, odd angles, etc probably starts to matter). Again, do it with your rifle and plug in numbers you think are accurate for environmentals, you may have a different setup, but at least on mine withthe conditions I used it might not matter. Now, if you were going to 10,000' and planned to shoot out to longer range, different story. My 6.5 dope below for comparison.
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