How to Engage Your Horse's Back

I found this on Eventing Nation and thought it was fascinating and super helpful! Can't wait to try these things with Limerick!

Now I'm comparing to the pictures of Limerick and Kristen.. he definitely wasn't engaged, but do any of you know how much butt-highness will affect the engaged appearance of his back? He is incredibly butt high, so his back might always look hollow..? 

LIGHTBULB MOMENT!! I see it :)