Hmmmm. Thanks for sharing the Ukulele Mike video
@ailevin and also to
@ripock the "heavy hands" idea. But I'm not sure if I do either of those things. I mostly think of it as using leverage.
In the video, Ukulele Mike is keeping his thumb "properly" placed on the back of the neck right behind the barre formed by his index finger and his explanation focused a lot on increasing muscle strength to hold down the chord and make it ring clearly.
When necessary, I tend to create more leverage by extending my thumb along the back of the neck towards the headstock. I think I am unconsciously moving my thumb to increase the length of the "moment arm" and generating more torque to hold down the barre and the fretted strings without using a lot of extra grip strength.
Any thoughts on this? Maybe I will have to shoot a quick video to explain?....