I think @CanteringCarrot above made a good point: you might need to step away from looking at just the back as you watch the tests. The back is a little more of a dynamic situation than just how dropped or elevated it seems - you also need to factor in the elasticity, how much swing is there, and even if it doesn’t visibly seem elevated (IW’s Don Johnson is a horse that might not give the perception of an elevated spine, for example) you need to keep an eye on the hind end. Even if the back isn’t up, how much weight bearing is occurring behind? And if there’s weight bearing, is there also impulsion occurring? And if both of those things are occurring, is there also swing/reach, and is the back soft and supple enough to carry all of that energy to the front to help lift the front end?
These are just a few things that I can think of off the top of my head.
One thing to keep in mind is that while Weighold is (I believe) IW’s highest scoring horse, she has entire stable of them she goes out and rides test that score very highly (and can on a good day, win) with. While there’s definitely a trend of popular/fad riders (and horses), that’s one distinction with IW. She puts in a good ride on a number of horses and is scored accordingly.
One of the things that she does very well, despite some of her horses having some more interesting conformation (Don Johnson is a good example of this, again, but even Weighold is a little odd to me - and she doesn’t have most bombastic gaits, either) is that she goes out and puts in a good ride every single time. Her sense of geometry for her tests is impeccable. Likewise, her timing in aids is really hard to match. She sets her horses up for each movement so they can perform with the necessary dynamism and elasticity to make the movement both technically correct, but also following the tenants of the test.
Edit: I will also suggest that you work on training your eye to follow what a horse’s hind end is doing. I think some of the recent trends for the front half of the horse (flashy front legs, that the head/neck is doing) have distracted us from seeing what is happening on the back half. And I generally adhere to the tenant that everything is going to start from the engine - if a horse’s hind end is elastic, weight bearing, has reach, and is dynamic, you can learn to track how that is shaping the horse back to front (and how it may impact things like the back, the carriage, freedom of the shoulder, collection, etc).