Textures Unexpectedly Downsized on Quest 2

Background:  I have a material that uses an 8K x 4K texture like a cubemap using the LongLatToUV node in UE5.1.  There is a user-controlled surveillance camera in a static environment, and rather than render a virtual camera into a render target to display on the surveillance monitor, I'm using this 8K environment map generated from the position of the camera mesh and then doing look-ups into it based upon the world orientation of the camera mesh.  The user needs to be able to zoom in fairly far and retain clarity, hence the large texture size.  This works very well in PCVR mode, but when packaging for the Quest 2, the texture gets downsized to 2K x 2K and is obviously quite blurry when zoomed in, especially horizontally.  I created a new material that uses two 2K x 2K textures (the same 8K x 4K, downsized to 4K x 2K and then split in half) to effectively create a 4K x 2K texture on the headset (see image below).  The worked perfectly.  I was then confident I could use the same tiled cubemap technique to effectively create an 8K x 4K texture on the headset.  The end result looked exactly the same in PCVR as the original 8K texture.  On the headset, however, it looked exactly like the previous attempt, 4K x 2K tiled, making me think my eight 2K tiles got downsized to eight 1K tiles maybe.  Does anyone know why this might be happening?  I'm assuming there is some kind of per-material limitation that I am running up against.  And thank you for taking the time to read all this!

(Note: the material has an additional texture look-up to create a HUD effect, so Option 1 has 2 look-ups, Option 2 has 3 look-ups, and Option 3 has 9 total look-ups.)