@Vietfox

The third reagent is redundant. It does not add any benefit to the benefit of the other two. There is no reason to believe that it should increase the duration of the potion.

Usually, when I see a difference between (a) the duration during which a combination of reagents provides its benefits, relative to (b) the duration of the same benefits that a different combination provides, the difference in duration is probably the result in implementing the software (i.e., a "bug").

On the face of it, the difference in duration appears to be an error in the tooltip for one of the combinations. In my observation, the duration is not different in actual use of the respective potions. I assume the same applies to poisons as well.

(I play TESO on PC NA.)

Vietfox wrote: »

....
When i combine Nirnroot, Blue entoloma and Namira's rot i get about 2 seconds more of invisibility than if i combine just 2 reagents, that's why i was asking.

Have you used an add-on that records Combat events in a "log" form? That is the ony way of which I know that might record the data in some form that could enable us to determine whether a character actually does gain more invisibility than if we combine just two reagents.

If I recall correctly, there is a combination of reagents for an Essence of Health IX (-?-) for which the duration is two or three seconds longer than for other combinations that have the same benefits. However, I have never verified whether the duration is the number of seconds, stated on the potion's tooltip, when the potion is actually consumed by a character during play of the game.

Whether making any potion with three reagents instead of two, or with a different combination of reagents, might actually increase the duration of its effects, I don't know. But I haven't read anything about ESO combat which contained any remark about it. Nor can I recall reading anything about Alchemy which contains any comment about it. Perhaps the additional time has been overlooked by others, or perhaps the additional time is an error in the algorithim for determining the effects and duration of the potion.

Which is to say, there may be a bug in the software because there is a flaw in the algorithim for determining the benefits and duration of a potion. Or it might be an undocumented intentional aspect of the Alchemy feature.