Here is a Method That can Help You with Difficult Level Sensing

Turn a capacitive proximity sensor into a level sensor. This is ideal for tanks and vessels that you cannot drill through the side for mounting.

Wrap bare wire around the sensing head and extend it to the length you need to detect. Insulate the wire using electrical tape all the way down, but leave the end exposed. This acts like an antenna. Anything touching the end will now be detected. I have used 14 and 12 awg wire, depending on the application.

This is ideal for hard to mount areas. You can bend the wire any way you want as long as the insulation (electrical tape) is not exposed.I have had the wire extend up to 30 feet from the sensor without an issue.

Some quick information about capacitive proximity sensors.
A capacitor is defined as two electrically charged plates separated by a dielectric. In the case of a capacitive proximity sensor, the dielectric is the material that you are trying to detect. As the material moves closer to the electrostatic field of the sensor, oscillation begins. It will get past a threshold and trigger the output to switch.

Some common dielectric constants for material:
Glass - 5
Wood - 2.7
Paper - 2.3
Air, Vacuum - 1
Water - 80
Once you know the dielectric constant you can determine the sensing range (Sr) by a chart that usually comes with the sensor or in the manufactures manual.

Example: Water is 80 so the sensing range is 100%

I generally just try the sensor to determine if it will be suitable for the application.

If you have any questions or need further information, please contact me.
Thank you,
Garry