The manual for the moog says that middle C should be at 3.00v, and v/octave should be 1.00. This is certainly not the case.
Despite what the Moog manual says (or suggests) the Slim Phatty does not operate at precisely 1volt / octave.
I think the correct setting is 0.97, but don’t take my word for it - you’ll need to experiment a bit to find the correct value. Once set, it should work as you expect.
There are a few threads on the Moog forum about it.
http://forum.moogmusic.com/viewtopic.php?f=7&t=11456