That’s an interesting point.
I think that, since Japanese is so full of homonyms, odds are pretty high that the reason my answer matches another kanji isn’t because I got the two kanji confused visually, but more out of sheer coincidence. Getting alerted in those cases, amounts to being given a random fact: “Hey, did you know that the reading you typed also happens to match another Kanji that looks nothing like this Kanji?”
That’s potentially interesting information, but it doesn’t exactly relate to the core reason why I love the 丸⬄九 feature of the script, which is helping to identify points of confusion between visually similar Kanji.
I admit, I can also imagine cases where I completely mixed up two kanji that look nothing alike - perhaps I entered こい for 愛. In that case there really was confusion, but I’d argue that’s: (1) probably the minority of cases, and (2) actually a different type of confusion than 丸⬄九.
I’d propose that a minimum level of visual similarity be required for alerting on 丸⬄九 and if it seems worth the effort, a different, optional alert type be added for something akin to 恋⬄愛
But all that said, I still massively appreciate the effort you’ve put into this script, and will happily use it as-is. I can always just configure the setting to minimize the popup by default, and treat it more as a “pull” than a “push” system!