I don't think you're taking everything into account with those swings. For example, the left swing's tendency to hit a player in the head at the start of the animation. So more often than not, you can hit your opponent outside of your sweet spot and not glance with a left swing, as long as you hit them in the head(which happens the majority of the time). You can do the same with a right swing, you just have to go out of your way to aim for your opponent's head.
Next, it would appear that the first 120 degrees or so take less
time than the next 120 degrees, where the animation(weapon velocity) then slows down yet again for the last 30 or so degrees. Without the tip of the weapon moving at a stable velocity around the body, you can't compare similar angles of different swings in a meaningful way.
When keeping these and the previously mentioned things in mind, it should make perfect sense as to why the right swing/polearm left swing have such a tendency to glance. Look at the Pole left swing, it covers the first 160~ degrees very, very quickly, then slows down significantly to finish the last 90 or so degrees.
Edit: Furthermore, 1h damage(particularly cut weapon damage) is so low that you have less of an
effective 'sweet spot'. Any time you hit outside of your actual sweet spot, you're just asking for a glance(hell, you're asking for a glance simply by using a 1h sword).
Edit 2: Basically, Yes those are the areas where you are likely to glance but not necessarily the 'sweet spots'.
Might be the hand (i.e. weapon) position in the animation fooling you.
The 1h right swing is odd in that the weapon is angled back towards the forearm during the first part of the swing, so this could very well be a major factor here.