I've found that option virtually worthless. No matter what I set it to, the dashboard grabs some of the space, leaving me with less than 2 lines. Pretty crappy when many Pro|E messages are 2 lines.
I opened a cal with tech support on this a year or two ago saying it was broken, it didn't stay at what it was set to. They, of course, said it was intended functionality. It only sets the initial visible lines.