One thing that may be part of the problem is that in your dimstyle, the Orient toward reader… setting is checked, meaning the text will be adjusted to be readable in a specific viewport.
Try unchecking that and see if it makes more sense.
If your viewport is anything other than world top coordinates, that is especially significant.
How are you using the xform you get from GetTextXform()?
You use DimensionStyleFromId() which returns the parent dimstyle. If there are property overrides, that will be different than the effective dimstyle for the annotation. I think the only override in your case is TextHeight which won’t cause a problem here, but in general, you should use