Do you use a metronome? My consistency improved greatly once I began using one.

One thing I've noticed about Michael's printing is that he 1) starts the metronome, 2) covers the printing frame with a big cardboard sheet and turns the lamp on and 3) waits a couple of seconds before removing the cardboard. In this way he knows that the lamp is always burning at the same maximum intensity when he begins exposure. Likewise he stops exposure by throwing down the carboard to cover the frame and THEN turns the lamp off. The results are remarkably consistent. He also uses a cadence of 72 beats per minute instead of 60 so that the effects of missing the beat are attenuated.