Aussie Truck Mirrors on LC200

We're busy getting our new Landcruiser VX ready for our 4 month trip across the North and West of this fine country. I've just tried to fit my Aussie Truck Mirrors (which worked really well on our Patrol) and am a bit concerned about how they sit.

As the strap is tightened, it appears that the two clips which slide into the window slot do not sit well, and the mirror arm actually rocks fore and aft. If I look into the window slot there appears to be one or maybe two layers that sit on the outside of the glass, and these finsih just below the outer rubber window seal. I think these do not allow the clips to bed down the way they used to in the Patrol.

As I tightened the strap further to minimise this rocking, the clips sink into the slot better, but there is still a small amount of rocking, and the outer window seal begins to get very distorted.

I don't want to damage anything - we've only had the beast for a week!

Has anyone else had this issue with ATM towing mirrors? And if so how did you overcome the problem so that the mirrors are held firmly?
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Cheers
LES