Okay, I'll write a little bit about what I know.
First of all, there's a certain art to edgeguarding spacies, and I've reached the conclusion that it's not possible to have a single flowchart that'll work every time. Instead, you have to make a read. It doesn't have to be a very hard read, but there still needs to be one. Your options do change with height and distance from the stage, like you said, and in a lot of scenarios you can cover a lot of the spacie's options with a few things from sheik.
With that out of the way, I guess what we're trying to do here is nail down the best thing to do with no baseline for how the fox is going to recover, correct? There's not much else to do, so edgeguarding with no baseline of expected recovery it is.
I was going to write some about back-throw at low percent, but just don't back-throw at low percent unless you know how they're gonna recover. Most of the time they'll just get the ledge for free or get back on stage, as it's really ****ing difficult to cover their options at low percent without a crazy read. If you REALLY want to back-throw at low percent, just short-hop needle, and try to cover what they do. If you don't like to needle in this scenario, you can instant short-hop bair which will stuff a quick double-jump. If you don't think they'll instantly double-jump, you can run off double-jump nair, to stuff a double-jump sweetspot or a quick side-b. Those are the fast options, and the ones you would want to start with if you back-throw someone at low percent with no baseline of their recovery pattern. If you think they're going to shine-stall or double-jump back, side-b, a short-hop needle wait-and-watch, while holding the needle, will let you cover those. I'm going to assume the reader knows what to do after hitting one of these, as after that the edgeguard gets easier, basically get the ledge and start bairing/nairing/fairing.
I guess I ended up writing about back-throw at low percent anyways, most of the time just go for a down-throw tech chase, as gimping at low percent with no read on how they're going to recover is really ****ing difficult, and not for the feint of heart.
I haven't really spoken about covering up-b's yet, and I'll go over that a little bit later.
Back-throw at mid percents:
Things get a little bit easier here, as you don't need to have an instant read on how they're going to recover, and a couple things get slower. First of all, the option of instant double-jump air-dodge is eliminated, so you don't have to cover that so much. Therefore, you can wait a little longer and see what they do, since back-throw doesn't put them very high in the air, a standing needle may be permissable, to test the waters a little bit. People get their scrubble jump caught all the time with this. A superior option, that requires a little more finesse, is the short-hop needle wait-and-watch. You can cover the same things that standing needle covers with a short-hop needle, it just requires better timing and faster tech skill for the follow-up. Run-off double-jump nair covers quick side-bs and you can downsmash if they tried to doublejump air-dodge while you were doing the double-jump nair. You can also regrab the air-dodge if you predicted it, or did the nair fast enough to have time. The nair has its problems as well, since a double-jump back side-b will sometimes beat your nair, since they can do it after the hitbox of the nair and before you can get something out. In conclusion, I think that short-hop needle wait-and-watch is the best here, but I haven't really found a way to make it work, yet. I'd like some input on the short-hop needle.
Back-throw at high percents:
Things get even easier and simple than mid-percents, the back-throw puts them even farther out, and up-b's become more popular here, as they can get a little safer sweet-spot to the ledge from how far out they are. The same options from mid-percent are good here, except you need to be extra wary of a quick double-jump up-b. As if you do the run-off double-jump nair, and they do a double-jump up-b outside of your range, you've lost the exchange. The only way you can continue the edgeguard after that is to run-off fair them going to the ledge, grabbing the ledge, or hitting them as they go onto the stage. All of these require good reactions or a read.
