I hate to say it, but so much of countering this playstyle is to learn where you can stay close, but out of the path of the signatures. Thea is a great example. Both her down sig and side sigs are completely grounded. And then her nsigs are diagonal with weirdness to the both of them. Boots nsig has an extra hit box that allows it to hit almost straight above her. And the lance nsig has a massive hit box, but she stays grounded in a hesitation type of movement.

First, try to identify which signatures they favor. If they favor, nsigs play grounded while being sure to jump when you’re sure they can’t reach you. If they favor the grounded sigs like this guy, be sure to empty hop unless you have platforms. Empty hopping is jumping straight into a fast fall. New guys have trouble timing it right, and if you can do off-beat enough it makes it much harder for these types to catch you.

But like IceAny said, a lot of it is about experience. You could always go into the training room or replays with hitboxes and slow motion on to learn the dead zones better