Bending with your knees helps in a few ways in my experience.
I found that the more I bent with my legs the less it shifted in general.
Also, if your carrying past the 3 o'clock position and you bend over, your shirt may get hung up on the holster causing greater chance of exposing it.
I've seen it happen twice at a grocery store years ago.
The 1st was a guy wearing a Hawaiian shirt (unofficial retired guy concealed carrier uniform) who bent over to get some oatmeal. I just happen to be going down that isle and could see 1/2 of the holster while he was bending over and his shirt didn't drape back over it when he stood up. I quietly said 'fix your shirt' and motioned my hand behind my back as I passed by.
The other time was in line at a grocery store. I came up behind him in line. Practically the whole gun was exposed.
Pay extra attention when getting out of a booth at a restaurant, too.