gonk and avfan, the bottom of my 50in plasma TV is 55in from the floor, i'm sitting 13ft from it and the TV is tilted at 15 degrees.

1.At 13ft viewing distance what should be the ideal tilt angle?

2.Secondly, it seems that i won't be able to change the tilt angle that easily anymore so if it is stuck at 15 degree tilt what is the ideal seating distance from the TV because i can adjust the distance i sit from the tv?