I had the exact same problem, esp. with pass thru, and when using my rotary.  Amazingly you only need about an inch to get below front bar.
I didn't want to mess with the head, so found this to convert from smaller 18mm tube, to larger standard 20mm.  
This allows me to lower my nozzle by 1.5 inches.
I was gyped, is now $2 cheaper.
https://www.cloudraylaser.com/products/ ... 5c86&_ss=r
Then I added a normal 20mm nozzle with 90° air assist tube.
I also used a 20mm meniscus lens w/50.8mm focus inside the larger 20mm area prior to screwing in the M22 nozzle.  This allows me 5mm focus below the nozzle hole.
In the pic you can see that the nozzle is below the front bar, and then add another 5mm gap for focus to top edge of material.
You can also see in my pic where I can replace my rotary wheels with some 3D printed holder I designed for baseballs or pencils.
Works great for me, hope this helps,
Cad
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