Projectors should be placed where the lens demands that they be placed at all times. This can be tricky to accomplish, but is there some reason why you think that this is something that you will not be able to accomplish?
The lens should be dead center to the screen. If you are off by an inch, with a good screen, you won't notice.
The lens of the HT2050a should be about 3-6 inches above the top of most screens (shoot for 4 inches) and centered on screen.
There is no reason with a good projector mount, and a good tape measure, that there would be any issues doing the installation properly and getting the projector mounted exactly where it needs to go and at the proper height.
Most people have said that the 2050 is the better choice over the 3050. No way I would spend the money on the 3050.