Tbh, I would never mess with the bounding box value and set it to anything other than the player's defaults if you can help it.
I saw your video and I understand your model isn't the same size but this option is really glitchy.
I've tried playing with this when I was looking into options for making players not collide with each other. The farther you get from the default, the more you start to get stuck, fall through bricks, miss collisions. I'm not exactly sure why this option is so buggy, but the last time I used it it was.
Also did you try looking at a different player type, like the womprat or walle? Do those use different bounding boxes?