My car's normal cold coolant level is just a slight amount -below- the low mark on the reservoir (the "cold" level mark). When the car is hot the level goes up to about 75% between the two marks. I was a little concerned that this was too low a level, but some investigation on the web seemed to indicate that each car finds a level at or near the low mark and then stays there, even if it is slightly below the mark. What I read was that adding coolant would not help as the car will simply re-adjust back to its own nominal level. That is exactly what I experienced -- I added some coolant, the level was high until after a long drive, then it was back to just below the cold line after the car cooled. This is all my interpretation, so YMMV.
I don't know if that info helps you or not. And by "just below" I am talking about less than 1/4" below the line -- my level almost touches the bottom edge of the line.
