Re: Gripů wait for me!
As a BJJ player, gripping is my life! I live (and die) by it.
Couple of folks already pointed it out, gripping for this kinda technique is actually best done with the palm only without the thumb.
That said, your body position and wieght distribution is also important as well as the orientation of the grip, and eventually, you have to do something with that grip that moves you to a positon of greater control.
A little hard to describe here as much is dependent upon orientation of the situation, but maybe try to play around with "thumbless" gripping some to see if this helps you at all.
I know in aikido alot we use full hand thumb grips to train...there is a reason for this I think as it encourages musubi...so keep that in mind as well. If uke is pulling away from you, you probably are not giving him a good reason to stay connected! Remember uke, is always right! so keep working at it to see what things you can do to stay connected...that is the practice anyhow!