Reverse Parking Sensors - Correct Parts?

Hi. Two of my rear sensors packed up ages ago. Never got round to fixing it as it was no bother. Had two recent "reversing incidents" with low walls so I thought I ought to get it fixed.

Ordered and now have two sensors from theBay. Apparently the correct part as per extensive searching.  "Rear PDC Parking Sensor for Skoda Octavia 2004-2013 7H0919275C"

The sensors on my bumper seem to have a "Shroud" or "Cowl" around them as per the lower pics. When looking at my sensors it seems that only the inner circle of the sensor part is visible. Is the outer ring hidden by the shroud? I'm worried they wont fit. It's a complete bumper off job as I have a removable tow bar fitted and there is no room to get a hand up inside to test fit or anything.

Any advice would be most welcome.