I find stitch-in-the-ditch really hard to do. On the few occasions when I attempt it, I use a walking foot. I would find it impossible to do stitch-in-the-ditch with a darning foot.
The darning foot does ride higher than other feet, to allow movement of the quilt. It would be used for free motion quilting.
It sounds as if you may be using a darning foot to do stitch-in-the ditch. If so, that could be your biggest problem. There are accomplished quilters who can do SID that way, but it's not for a beginner.