Well, the stresses on the reed when playing will tend to make it collapse into the mouthpiece window; furthermore, the reed is wetter on the flat side than the curved side; so you will periodically have to go back and flatten the back of a reed.
On baritone I usually find I've got to go back at least one time and re-flatten. After some weeks, though, they seem to stabilize.
Personally I just use a small penknife and a small straightedge. Same knife I use to adjust the strength, side-to-side balance, and adjustment of tip vs. heart vs. shoulder areas. But what do I know? I'm an old fart, who learned reed adjustment back in the day when it was considered standard practice for all single-reed players.
I'm not really sure how you get the back of a reed flat by sanding, if it's out of flat by 0.020" as I've commonly seen, without sanding down the back of the tip to nothing, or trying to hang the tip off the sandpaper and not accidentally going over it, plus people are typically recommending these super fine grits that will take you HOURS to flatten 0.020", and furthermore if you've ever tried to lap a convex surface you'll find that it's real real easy to make it worse, because it just rocks on the high spot. On the other hand, flattening the back with a small knife allows you to remove material exactly where it's needed, and not where it's not needed.
On baritone I usually find I've got to go back at least one time and re-flatten. After some weeks, though, they seem to stabilize.
Personally I just use a small penknife and a small straightedge. Same knife I use to adjust the strength, side-to-side balance, and adjustment of tip vs. heart vs. shoulder areas. But what do I know? I'm an old fart, who learned reed adjustment back in the day when it was considered standard practice for all single-reed players.
I'm not really sure how you get the back of a reed flat by sanding, if it's out of flat by 0.020" as I've commonly seen, without sanding down the back of the tip to nothing, or trying to hang the tip off the sandpaper and not accidentally going over it, plus people are typically recommending these super fine grits that will take you HOURS to flatten 0.020", and furthermore if you've ever tried to lap a convex surface you'll find that it's real real easy to make it worse, because it just rocks on the high spot. On the other hand, flattening the back with a small knife allows you to remove material exactly where it's needed, and not where it's not needed.