I do not know of any articles but to get good knee bend you need to get your off leg out and doen to the side of you. The more you push your non sliding leg out the further your knees nd hips go down.

 Instead of reading about it just go and practice the last coulple steps pushing into a slide and getting your off leg out and the sliding knee will automatically bend

I used to have the problem of inproper knee bend, so that I'd tend to plant the shot (with fast feet included) and bend forward with poor release leverage.
I got the tip from an experienced local player to try to start my approach in a half-sitting position, knees already flexed but with an upright upper body.

Looked and felt wacky - but it helped me a lot to get used to the flexed knees, getting down at the foul line and shifting the body CG back so that I'd avoid the body bending. One of the hot tips that really improved my game.

Practiced this for half a year as standard delivery and then began to start in an upright adress position - with foot speed control I found it now easy to get down and into a slide (mine is now actually pretty long!) while staying upright and square with the shoulders. Leverage has improved, too.
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DizzyFugu - Reporting from Germany

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