I had a similar delima an solved with a low profile flat proximity sensor. An will in this post explain why I chose this new style proximity sensor.
In the photo below the White mount is a thumb screw adjustable Mounting block, my Proximity sensor a TL-W3MC2 using 5Vdc.

TL-W3M 3.jpg

As you can see I mounted the proximity sensor behind the X-Axis bearing mount, then using a design that was already created, I re-designed to more suit my needs.
Allowing the low profile shape of the new proximity sensor to be mounted within 15 mm of the nozzle, though I finally decided on a 25mm distance.

By looking at the image you posted I would venture to guess that your Proximity sensor is about 65mm from the nozzle, and shorting this distance would be beneficial
Using my logic I somehow decided against this same design by the manufacture of my 3D Printers, having the sensor the same 65mm distance away from the nozzle.
An am happy with my decision as the auto bed leveling correction has never worked better.

Spring tension thumb screw mount
TL-W3M 1jpg.jpg