For what it is worth, i use an older NH 467 moco, which has a 7 ft bar. I have found that new guards and sharp knives are essential for good operation, but that plugging will happen, especially in lodged conditions where the material is all tangled. If there is a lot of dead material (common in an uncut field), this also contributes to the problem.
I have also found plugging next to the inner shoe can occur if i do not pay close attention to where the mower is tracking and I wander into cut material.
Brad