Yeah one flag between 100 and 600 is going to be insignificant and frustrating if you’re trying to learn wind, it’s simply not going to give you a complete picture of what’s really going on. Think of each flag as a old timey sensory device that can give you wind speed and vector but only at the position it’s placed. Unless you’re shooting across a perfectly flat plain with nothing for miles around there will be localized effects that you’ll want to be aware of both in dept, width and height. The more data points (that are properly placed) the better picture you’ll have of what’s going on.
Once you’ve developed an understanding of what the wind is doing based off you sensory array, then you can start substituting the flag for near by observable environmental effects (mirage, vegetation, dust, etc.). This is important especially if you ever plan to shoot anywhere else. You never want to depend on just one method because there will enviably be a time when your preferred method is unavailable.
Example, I shot an F-class mid-range match (300y/500y/600y) last year, there was only two wind flags, one at the targets and on at the 300y. The 300y flag got tangled up around the pole and mirage was difficult to see. A lot of shooters did well at 300y and cleaned it but the struggle began once we moved to the 500 and 600. Most F-class dudes lean heavily on mirage and flags, because it’s incredibly accurate. When those methods were unavailable it hurt them. I ended up winning that match with a 598/600 using a 5.56 gas gun (F-class isn’t my normal discipline) I’m not trying to toot my own horn, as I’ve know given normal circumstances 3-4 of the other competitors there that day would clean it, however the lack of diversity in wind reading can handicap you really quick.