Problem solved. It appears that I do need to use a “transform” to explicitly transform my glTF content into the geoframe. I mistakenly assumed that their might be a default transform to take you from global to local coordinates within a given region. For example, it maybe assume East-North-Up and that the south west corner would automatically correspond to the local glTF origin. I could have sworn I tried adding my own explicit transform and it didn’t work, but I just circled back this this and it did.
In hindsight, it makes just as much sense to not assume a default transform for any of the bounding volumes.
See Omar’s comment in another thread to basically states the requirements for bounding volumes and the underlying content.