I've been taught to sit when the horses outside leg moves forward but it's the same as rising when the horses inside led is moving forward aswell. And then if you realise your on the wrong diagonal sit trot for 2 beats and rise again
Hope this helps😊
A phrase many people use is "rise and fall with the leg on the wall". Which simply means with the front leg of a horse is closed to the side of the arena goes up; you go up and when it hits the ground again, you go back down! Hope that helps!