Fantastic writeup! I'm finishing up a 91 octane tune for my Revo turbo setup. I was planning to go 93 octane next, but going E30 was recommended by my tuner.
So I started to research ethanol sensors and placement and that's how I stumbled onto this post. The way the OP installed the sensor is how I plan to install my sensor setup. I plan to use a Zeitronix round gauge and mount it into the glove box. I already used a lot of dash space with the three gauges I've already installed, plus the ethanol content will not change unless I add fuel. So constant monitoring for me is not needed.