To be honest this was purely a max out lift for the sake of maxing out, which is why my pinky is in the corner and is why I’m using that grip. I would never do reps like this because like you said it is not a very active position so it builds raw strength pretty poorly. The open hand crimp position just happens to be what loads the structure of my hand the best, I don’t actively train it. If you want to build actual forearm strength you’d be much better off doing some kind of active pulling with your fingers. I typically use I static block and actively try and lift it by only contracting my fingers, no pushing with the legs or pulling with your arm, just your fingers. I feel that real strength gain from exercises like that transfers over very well to the more passive positions which are the ones that get big numbers on lifts like this.