question on mounting the new magnetic filament monitor

[duetal]

Hello - I just ordered the magnetic filament monitor https://duet3d.dozuki.com/Wiki/Duet3dFilamentMonitor_RotatingMagnetVersion#Section_Before_the_Extruder

I have a stupid question about this part in the manual: it can mount directly onto the PTFE filament guide or bowden tube, held in place by the collets and collet clips.
Does the filament inside the monitor has to be exposed or can it read the filament inside the PTFE tube?
I'm using Railcore II 300ZL and i have a PTFE tube going from bondtech to the spool holder. So mounting this on PTFE tube would be nice. Here is a picture of my current setup:

[samlogan87]

Hi there,

Where did you buy yours from?

Regards,

Sam

[duetal]

Filastruder has it