[ibrokeit]

Okay - that seems to work 

As for silicon - it is a practical solution with little expense, and you won't have to get/make something custom (from scratch or customizing another part).   Don't know how it would react to body work and/or how it long it will last (UV, heat, vibration, etc.) - possibly someone will know what is suitable.   As for look/styling not sure - if black silicon it probably isn't going to draw much attention... other colours might.

While still running with the silicon idea... though it would up expense slightly... maybe see if you can get some black PVC pipe that fits the hole in bumper (I would suspect if it did so reasonably tightly the sensor would sit on top of the other end.  Would require less silicone and colour of it probably wouldn't be noticeable - downside is it would require someway to feed the wires thorough the short piece of pipe.

[Phil №❶]

You could try plumbers pvc pipe and have it coloured the same as your existing paintwork. It comes in various sizes.

[Dazzler]

Or use clear silicone, but for what you have paid you really shouldn't have to do this...

What did the installer say about Alan's mention of reprogramming them? Can you ask him questions by email or something?

[Shambles]

... for what you have paid you really shouldn't have to do this...

Echo that.

They're either not working to spec or not fitted to spec. Either way, they're not fit for purpose...

[cruiserfied]

 

You may as well have fitted them yourself at this rate.

[nangers]

Thanks for all these suggestions, as there is quite a high chance that the installer would not know what to do himself ................ that's what I am preparing for anyway.

[Dazzler]

I think a substantial rebate or discount is in order.

[nangers]

I am posting an update to the resolution to my problem.  I decided to not wait for my installer as he is on holidays for another month.

So I went to Supercheap Auto in the hope of finding a rubber grommet.  It turned out that they had an exact grommet size that fit the sensors perfectly - 3/4 inch.

http://www.supercheapauto.com.au/online-store/products/Champion-Wiring-Grommet-3-4-Handy-Pack.aspx?pid=17410#Recommendations

Cost me $6 for 2 grommets.

Attached is a picture of the install.

Moral of the story - sometimes installing a better quality product will cause more problems than installing an lesser quality product.  In my case, installing a better quality sensor with wider angle of detection caused all the problems, whereas installing a cheaper chinese sensor with a smaller angle of detection would not have caused this problem.

[Phil №❶]

Good cheap fix. 

[ibrokeit]

Nice!  That looks good.   

I notice that number plate mount isn't mounted - and I suspect it will break your sensor fix if it was.  Have you put anything - like foam tape - to cushion the number plate from the bumper?  To reduce (potential) vibration and/or plate marking the bumper by movement (e.g. rubbing paint off or scratching).

In the long term I would be after the installer to fix it (once they return), but that is just me.   Course that also depends on if you feel they are able to do such.

[nangers]

I'm not worried about the number plate scratching the grill.  The number plate would always cover the scratched grill anyway.  To be honest, I really cant be bothered chasing up the installer anymore. I've put too much time and effort thinking about this to bother.  I'm just glad that I have sensors that work and if ever needed to be replaced, it is an easy pop out and plug in new sensors. 

Thank you to everyone here for all the help and suggestions. 

[edagrade]

I think the fault lies in fixing the sensor to the recessed part of the grille (that is how it looks to me). If that is the case, it is an epic blunder by the installer & should be remedied in full by the installer.
The sensor must be fitted to the most forward face of the area to be protected.