Hi Mark
That's odd. You can't move the focuser into the tube any further, correct? Normally for your elongated starfield, you could just add spacers like this to fix it, but that sounds like it would push you back and you can't then get focus.
https://www.testar.com.au/collection...8-spacer-0-5mm
https://www.testar.com.au/collection...m48-spacer-1mm
I've not heard of an issue where you can't get closer to the objective... hope someone here can help you (or I'd be talking to the manufacturer about it!)