That video is great! I don't know if I can do those exercises on Sophie, but I'll try and do some of them during my lessons (i.e. On nice and quiet school horses).
As for the striding, I haven't learned to count strides or anything yet. I just let the horse pick the striding once and then try to keep it consistent, which I'm sure is not at all what I should do but it's the best I've got right now. She did three strides the first time I did the line so I've just kept it like that
I see what you mean though. And she has been taking that second jump earlier lately, I'm not sure why since I haven't changed anything about it. I'm still trying to find the right balance of riding in between the jumps and relaxing over them.
Looks like Sophie is taking advantage of that freedom to choose strides, and is taking the easy deer-like leap. Do you know how to set obstacles or poles at a distance using your own stride?
The first part of this video shows how you do it:
(I know. I'm addicted to horse videos
It would be best to grab some ground poles and set them up for trot distance (three to four feet) put up just two or three if Sophie hasn't done trotting poles. Ride over, and figure out what her stride is. You aren't allowed to pick at her over the poles, just like you don't pick at her over a jump, she needs to find the space herself. Half-halt before the poles if you need to, since she might try to skip a pole or get quick. Later set them up at a canter distance (as you see in the video above) and play around with the distance a little to see what her natural stride is, and what changes you can have her do with that stride. Once you can do that all easily, walk yourself over and between those cross rails you have set up, and mark each canter stride with a ground pole, ride over your new little grid. You can strongly influence her to take the four stride if you have even one pole set one stride before the second jump. She makes a new stride when you feel her lead leg in a canter land (you can also peak down and see the shoulder come forward) or when a diagonal pair lands in trot.
If you don't have enough poles, you can make do by approaching the cross rails at a canter and, upon turning the corner toward them, start counting how many strides she makes up to the cross rail, and after. When you get a feel for how her strides are, try to feel the distance and count 3 strides before the jump. When you count the third stride, she should take off. You'll know if you started counting too early or too late; she'll jump before or after you get to 3. To change stride length, half-halt her 3 strides before the jump or leg her 3 strides before, but you need to know what it looks like when you are 3 strides away from the jump first. Haha... it's all a little confusing.
... I would keep a pole in front of that second x-rail, or scoot it closer, I feel that it's detrimental for her to be taking off so early repeatedly.
Definitely use some of the ideas shown in Yunis' jumping clinic video I posted, like some of the set-ups of cavalletti.