Dell :: XPS M1530 6-/9-cell Battery & Zalman NC 2000: Wobble

I got a new 6-Cell battery from Dell for the M1530. I had a 9-cell before. All is well. Only issue is, with the 6-cell, if I place the laptop on the Zalman NC2000, the foot rests are not even. The back right foot rest, is lifted and there is this wobble.

Now, I did check if its fine on a normal, flat desk and the laptop sits perfectly fine, even on all four rubber foot rests.

BUT - with the 9-cell, the laptop sits well on the Zalman NC2000 (and also on a normal, flat table!)

I am confused as to why with the 6-cell it doesn't like to sit evenly on the Zalman???

To summarize:

6-cell on a normal, flat table - all is well, no wobble.
6-cell on the Zalman NC2000 - Back right foot rest (of the laptop) is in the air, hence there is the wobble. * Why?

9-cell on a normal, flat table - all is well, no wobble.
9-cell on the Zalman NC2000 - all is well, no wobble.

By the way, the zalman itself is fine, sitting well on all four corners on the table or on any flat surface!