Excuse my ignorance, but I'm simply not visualizing this "horizontal cut then vertical." I'm aware that the grain changes on a tri-tip at various points on the cut, as illustrated in the one section of this forum. However, the bulk of the grain appears to run the length of the roast. So typically I have the roast in front of me with that length running left to right. I cut the roast with the knifepoint facing 90 degrees away from me, then 45 degrees to the side, so I'm going against the grain twice.
Could someone please attempt to elaborate one what you're specifically referring to? I'm really struggling with this. LOL Tri-tip seems like one of those cuts where, even cooking it to perfection isn't enough. The cut seems to be as important, if not more so, to achieving the type of bite/chew you're looking for when tackling what is otherwise a fairly tough piece of meat.