Fred, yesterday you reported a GP Texture registration error. Now you say "I have not been able to check out creating letters in GP - can't get that far." Since you have not defined any GPs for use with the texture of concern, its not clear what you mean by "can't get that far".
Re the files you sent, I see no issue with the GPs you have programmed. I will confirm that initially, using your .bgl files with FSX, the GPs were not visible. But a recompile of the .ad4 file fixed that - similar to how you reported the issue of a month ago was resolved.
What I do note as unusual is that you have created a flatten that does not include the ARP. Consequently, ADE has three, conflicting elevations to consider: ARP local elevation - which is higher than your flatten elevation, flatten elevation and ARP elevation. I'm not suggesting you have done anything wrong. But, you have given ADE an unusual situation to resolve - which, depending on other aspects of your system configuration, may not get resolved as you expect. GPs are drawn at terrain elevation. Given the potential elevation conflicts, it's not clear to me what that would be. The GPS may be below the runway surface - which is what you seem to observe.
If FSX:SE operates differently in this regard from FSX, there's nothing I can do about it. You just need to be aware and work around it (like including your ARP in the flattened area or, flattening to ARP local elevation) Nonetheless, since this appears to be identical to the issue we discussed a month ago, I suggest you attempt to use whatever procedure you confirmed worked then. Let's focus on the registration issue.