Got the fucking yoko-giri finally, on my first try. Subsequently nailed it 4-5 times each on both sides as if I'd been doing it for years. I was celebrating so much that my class made me a certificate on the fly and gave it to me "1st Consistent Yoko-Giri" , I'm going to have that fucker framed.
The issue was power. I just wasn't putting enough effort into the cut. This time I just let the shit have it and it went through no problem. My shinken cuts like a dream.
Next goal is the yama gata pattern, consisting of kesa - kesa/kesa/kiriage/kesa - yoko. Tried and got the first 5 just fine, but I'll need work on my kesa-yoko transition.