I believe the vanilla behavior may be overriding the upgrade chances, because with 32% quality in an assembler I have:

Normal -> Uncommon 32%
Uncommon -> Rare 25.6%

This would suggest an outcome (for normal) of 68% normal, 23.8% uncommon, and 8.2% rare, if the exploding chance of uncommon -> rare gets the full 25.6%.

However, after performing a broad test (at rare cap), with 32% quality, I I turned up 68,120 normal, 29,387 uncommon, and 2,704 rare. This would suggest a distribution of about 68.0% normal, 29.3% uncommon, and 2.7% rare, which would suggest that the vanilla behavior of 10% exploding chance of upgrades has overridden the 25.6% chance to explode from uncommon to rare.

If this is intended, it should be written explicitly in the information section, because the tooltip REALLY suggests that the vanilla explode chance is being overridden. I would also suggest making the tooltip reflect the actual exploding upgrade chance to alleviate confusion.

The mod alters the "next probability" numbers, which are 10% in Vanilla :
Normal is 10%
Uncommon is now 8%
Rare is now 6%
Epic is now 2%

This number is hardcoded to affect both the quality bonus from your modules, and the odds of getting a +2 or higher quality roll.

The behavior is as follows assuming 32% quality :
68% will roll normal
32% will roll uncommon, of which 8% will roll next quality > 29.4% uncommon and 2.56% rare or higher
Of these 2.56%, 6% will roll next quality > 2.41% rare and 0.15% epic or higher
Of these 0.15%, 2% will roll next quality > 0.15% epic and 0.003% legendary
Eg, with 100000crafts, you end up with 68000 normal items, 29440 uncommon, 2406 rare, 150 epic and 3 legendaries. In you example, without epic and legendary unlocked, you got a lil more rares, but your testing confirm the above numbers.

Now, what the tooltips says is :
- if your crafting normal items, you'll get 32% uncommon or higher
- if you are crafting uncommon items, you'll get 25.6% rare or higher (0.32 * 80%)
- if you are crafting rare items, you'll get 19.2% epic or higher (0.32 * 60%)
- if you are crafting epic items, you'll get 6.4% leg. or higher (0.32 * 20%)

I learned through experimentation what the actual behavior is, but the problem is the tooltip lists all of that information even though the recipe is already set.

So if I'm making an uncommon item with 20% quality, what the tooltip says is:

• Normal -> Uncommon 20%
• Uncommon -> Rare 16%
• Rare -> Epic 12%
• Epic -> Legendary 4%

What I argue it SHOULD say to let me accurately know what this specific machine is going to do is:

• Uncommon -> Rare 16%
• Rare -> Epic 6%
• Epic -> Legendary 2%

Or even more usefully:

• Uncommon 84%
• Rare 15.04%
• Epic 0.94%
• Legendary 0.02%

The tooltip confused me because I thought it was telling me the probability that machine would be upgrading each. I contend that since the tooltip lists the effects on a machine that has been set with a recipe, it should reflect that recipe's probability to upgrade. (Unless it has been set on like a smelter, that'd be more complicated.)