Zwift Hub indexing gears

I’m after some advice on my new zwift hub, every time I put my bike on the trainer I have to index my gears.
Running the same 12 speed 105 cassette on my bike and zwift hub .
What I have noticed their is a difference in the cassette position on both the trainer and my wheel thru axle around 1mm .
Don’t fancy spacing my cassette out on my bike to get it to match up .
Any advice would be appreciated

I would consider adding a 1mm spacer on the wheel assuming there is room to have the chain on the small cog without rubbing on the frame. I assume you have no spacer under the cassette on the Hub so you can’t try reducing 1mm from zero.

Hi Paul, it’s my only option I think but need to add the 1mm spacer to the hub.
The Hubs thru axle measures 5.2mm and around 4.3 on my wheel.

I think you’ve effectively found your issue though - you need to match the dropout to cassette spacing between the two. A micrometer will help determine the exact delta between trainer and wheel.

You’re right, I misread your initial question.