You can fill wherever you want to, or need to. Sounds like they're saying overfill, cause you'll use that up. Put the tape where you think the normal level will be. Take the picture of the meter when the water hits the tape. Once you take the picture, you can overfill all you want.
You want your end result number to reflect the volume of water your pool will contain most of the time. It'll always vary: splash out, evaporation, rain, whatever... you're looking for the average. And if it turns out later that you missed the mark, and the average level is two inches higher, or whatever: then let the pool evaporate to where you marked it, take a snap shot of your meter again, fill the two inches, take a second snap shot, do the math, add that number to your original number. Similar exercise if you marked it too high.
When you take the second snap shot tomorrow, you might measure and record the distance between the water line and some known thing (like the bottom edge of your coping). That might come in handy for the future.
It's kinda catch 22. Your average level will actually be pretty stable, determined by the autofill and how you adjust it. But you can't adjust the auto fill until after you have water in the pool!
Two take aways: you can use the meter trick to fine tune later. And none of this matters too much. You'll be doing your dosing calc's with a number that most pool owners never get close to.