To further get a handle on winISD, I would recommend watching the videos from Toid on his youtube channel and from DIYAudioGuy. There are a couple other tutorials I watched, but that got my feet wet.
For the box tab, you can tune it manually slowly or use the mouse like you did (where it created a big hump in response). I usually play around with it like a theremin until I get it close, then I fine tune by slight adjustment.
https://www.youtube.com/watch?v=LKUL_Q4JXbw&t=8s (example of theremin)