Print on its side, as shown in the picture.

I am using a drybox with the prusa xl so I dont have to store filaments after use.  The problem with my drybox was that the PTFE tube had too many bends and it was very difficult to load new filament.  To solve this, I mounted the filament sensors to the table behind the printer so there were fewer bends and an easier loading process.

Parts needed.

• mounting bracket
• m3 hex nuts x2
• original screws included for mounting sensors
• CLIK-mate cable extensions x2
  • https://www.mouser.com/ProductDetail/Molex/15135-0506?qs=jFK2DQXLaBzN1OZf0p2Rdg%3D%3D
• CLIK-mate female connectors x4
  • https://www.mouser.com/ProductDetail/Molex/503159-0500?qs=3OKVfsn1b5A33HKbe66Ncg%3D%3D
• 4.0mm OD, 3.0mm ID PTFE tubing for dry box → filament sensor.  This reduced the resistance quite a bit.
  • https://www.amazon.com/PTFE-Teflon-tubing-10ft-Allen/dp/B07B8CT1YH

Process:

• Use the existing filament sensor cables, but route them to come out the cut-out in the back where the wire bundles are for extruders 1 and 2.  
• Solder the female CLIK-mate connectors back-to-back to create a coupler.  They nest very well and the soldering was easy.  I filled the gap between the connectors with hot glue and then put heatshrink over them.  A coupler may already exist, but I did not find one.
  • If you choose to not couple to the existing cables, you will have to re-pin the extension cables.  They do not work as-is.
• Connect the coupler and the new extension cable.
• Secure the sensors to the mount and place the mount wherever it is needed. 
• Reconnect all of the PTFE tubes.

You should have a straight shot from the dry box to the extruders with much less resistance.