2 points: Sweep (from bottom to top), Knee-on-Belly; 3 points: Guard Pass; 4 points: Mount, Back Mount (back-control with hooks/body-triangle)
Why people argue about this
People often think that positional points are awarded for simply getting into a dominant position like mount or back-mount, which is incorrect. Actually, these points are given specifically for sweeping from bottom to top, achieving knee-on-belly, passing the guard, or taking the back after being in those positions, not just for occupying them.