I'd like to install an optical sensor to detect when my RO reservoir is as full as possible. I wish I could install one in the top of the container, but i know that pointing one down might cause false triggers from droplets collecting at the point of the pyramid. So I'd like to install it pointing upward, but as close to the top as I can.

If the tip of the sensor is touching a wall, will that trigger it?

Same question, but slightly different use case: I was troubleshooting the sensors in my ATK bracket a couple weeks back (the 'high' sensor was reading as CLOSED when it was out of the water). I have a small sump, so had the bracket installed so that the sensor tips were close to the clear acrylic wall (probably less than 1/4"). I changed several things and finally determined that the sensor had failed. I haven't gone back in and moved things around again to properly test if a good sensor triggers when close to a wall. Thought I'd check here before tearing my gear apart again in the name of science. :-)