Just to confirm - the starting point should be at the "beginning" of the runway approximately on the numbers and the aircraft should be showing a heading the same or as close to the runway designation?
Yes, this is how they normally are being made, and how we made them in the AFCAD that comes with the scenery.
Do you have any other suggestions?
The usual: check with the FSX airport scanner if you have other AFCADs for KIAH. And, even if you don't, be sure you are using the AFCAD WE supply with KIAH. For example, there's one you can download from the forum, but it hasn't been made by us, so we can't vouch for its correctness.