3 units? What's that? I've never noticed any settings on the 250 or so 738 aircraft I've flown. Anyway, some seats are more worn than others, some ratchet settings are missing etc, so I have to find my seat height, distance and pedal positions by trial and error on every flight.
Seat and pedal position is a personal choice. Some pilots like to sit upright, others like to sit lower. Provided you can see out of the window, I don't see why you shoudn't stick to your old system. The only caveat is that a flap 40 landing necessitates a slightly different seating position.
However, if you aren't sat comfortably you will struggle.