Crafting 5x vs crafting 1x to maximise your chances of free extras?

I'm trying to figure out if it's better to use the 5x for crafting and cooking. This is a quote from the wiki page for Crafting skill:

The Crafting skill has the following effect, proportional to the level:

Up to a 25% chance to craft an extra item, it applies only to items that can be stacked in the inventory. Notably, armors and wielded weapons are excluded.

Using the x5 crafting option is even more advantageous, as a cumulative mechanism adds even more additional items. Possible yields are +1, +3, +6, +10 and +15 (instead of +1 to +5 by crafting the same 5 items 1 by 1). This results in an overall +37.5% extra item at max skill level.

The page for Cooking says basically the same thing. I'm just wondering if anyone can verify this from their experience or testing? Because I don't think I've ever seen anything more than a +1 from using the 5x craft option. What exactly is the 'cumulative mechanism' mentioned? Is it saying that it does 5 RNG rolls and if it hits twice you get +3, if it hits 3 times you get +6 and so on? I'm just surprised that I've never seen this proc if that's the case, but maybe it's because the skill doesn't get very high in a typical run.