I upgraded my Ender 3 Max to use the BIQU H2 V2 extruder.  I had also purchased the BIQU Smart Sensor and wanted to mount it as well.  I found a few models, but they either mounted directly above the extruder (adding a lot of weight) or where my filament was not going to go.  My filament is mounted on top of my printer.

There are 2 models; one longer than the other.  It all depends are how far from the top rail you wish to enter the sensor.  I found the short version to line up better with my filament reels.

I printed these using PLA+, but you could likely use any PLA, ABS, or PETG filament.

I sliced these for layer height of 0.2 mm and added support for just the slot area.

Mount to 2020 rail using 3 3 mm screws and 3 mm T Nuts.