The ups and downs of adjustable straps

Recently I've been pattern making and with that I've been testing out adjustable straps. I first heard from my mother who frequently watches Nancy Zieman's show that you could make adjustable straps without any hardware. This idea greatly intrigued me and as she tried to explain the process and I tried to absorb through drawings how this was done. I was left curious and went to the internet to find more. I found a blog that sung accolades to Nancy and attempted to explain the process in pictures. I tried this process on the next bag I was making since I wanted my strap to go across the body and unfortunately it failed. The straps did not stay where I adjusted them, they worked they're way out to the farthest point as I walked. The bag that was snug to my body was now bouncing around my knee very awkwardly.
I don't want to call out this other blog but after my fail I reread her instructions to make sure I had followed them to the letter and even read down the comments and noticed other people had the same issues I was having with the straps. I searched Nancy's site with no answers or videos on this process.
I can only think that there must be something missing from the instructions, that perhaps this other blogger had miss interpreted the instructions. Without seeing Nancy's video myself I can't be sure.
I did however make a second bag and strap attempt making adjustments to the dimensions and after testing it at home I was almost certain that I had it figured out but when I took that bag out into the real world it also failed.
So I suppose in the end this post is about lessons learned. I think the next time I hear about  "adjustable fabric slides" or "no hardware adjustable straps" I will be cautious. The two bags I have already made I will have to top stitch the straps at my desired length to keep them in place. I'm still frustrated by this. But I am glad however that I tested on myself first and I didn't make any of these up as gifts I would have been mortified.

In case you were curious. First and second strap attempts...

Thanks for reading♥ Olivia