My first baidarka (a 14' off of brinks website) had a tendency to lift the bow if I sat at the back of the cockpit. Sitting forward about 6 inches evened it out, or hucking lunch in the front. I find I purposely slide back if I want more maneuverability, forward if I want more tracking/speed.
My 16' aleut based on the 14886 on zimerlys page is pretty balanced, I sit about 4 inches forward of the back of the cockpit.

Generally speaking, put a dowel on the ground, put a board on the dowel, sit on the board with your legs extended, same position as in the boat. Roll the dowel forward and back until you find your CG. Mine tends to be just forward of my hips. My boats even out when I put my CG right under the massik, but hull shape will change that some.

Oh, and I use a backband (actually a waist band off an army ALICE pack) looped over the ribs. By tying it to different ribs I can get different seating positions.