the bmw coolant bottle is a good idea but since I had the correct proximity sensor in hand i decided to give it a go and delighted that it worked as I hoped it would. I spliced into the wire from the C0223 connector as I still could not find the connectors in the engine bay but turned out better as it is all tucked in the fusebox area. the warning light comes on as it should and a road test did not result in any false positives. still need to try it in the offroad style inclines. SO far so good! thank all for the help!

Can you give me the type of sensor you used? Also take a picture how it is installed (how far from the tank and which position).
Thanks

So this is the sensor I used (normal closed type):
https://www.ebay.co.uk/itm/282940669176