never used rack pulls for thickness tbh, though they will help in that regard...
grip variations, Ive never played around much with those. YOu need to try difefrent grips (within reason obviously - i wouldn;t/COULDN'T use a snatch grip OR a super close grip on these) and see where you feel it, I guess.
Interestingly, I've observed that the poorest deadlifters (form-wise obv, those who throw too much back into it, round at the bottom, and don;t get enough leg drive etc etc etc) get the best benefit out of rack lifts from knee (the way bonez and others said).
Its all good as long as you';re moving more weight than off the floor (for bbing) and keep the strong back arch or whatever that means to you.