I'm not really sure if the difference between INFPs and ISFPs is really that pronounced. We both share Fi, and that's how I view and make most of my decisions about life.
For me, when I'm in my Se moments I get to tune out the thoughts in my head, and really focus on what's going on in the outside world around me. Whether it's working out at the gym, appreciating nature, or putting together a puzzle, I take it all in until I get overstimulated. It's really hard for me to describe because it's something I just do.
I'm not a fan of abstraction and theory. If I can tie in a practical application or think it out thoroughly, I can get it but it takes me longer than other people. It's not like I avoid it like the plague, it's just not as interesting to me as what I find aesthetically pleasing.