If the 70 yard shot is no problem then I doubt it's technique per se. That's nothing against the video but at some point you have confidence and lose it with a certain mental picture or situation.
The mental block is a good recipe for deceleration and geauxforbroke's idea is spot in IMHO.
Have you tried the goldilocks approach? One swing you know is not enough momentum, one swing you know is too much, take one in between and go. Something to distract your mind from the "problem" and get you to focus on the target more...
All these sub-full swing yardages appear to be feel related. I also like what @geauxforbroke stated about making fully committed shots with the weight forward and choking up on clubs to reduce distance.
I think the main thing is to get a consistent swing, then do everything he mentioned and practice a lot.
It appears to be a feel related issue more than a mechanics one?