I did stay at a Holiday Inn Express last night so, here goes.

>Does increased mana into conjuring go into:
>A) Increased servitor level (which I assume affects HP,
>Strength of Attacks and specials, "class" of servitor
>(transplendant, luminous, etc)
>
Yes, it can increase level which can change Angel, Archon, Demon, Devil's type and how nasty every conjurable mob considers. Lesser Archangel/Transplendant/etc being hooded, then going in reverse down.

>or,
>
>B) Increased duration of summons (I've never had one last more
>than 2 bindings, but perhaps that is possible?)
>
Yes it can also do this. As for why it's the first sometimes and this one others, I'd chock it up to luck. I've put in an enormous amount of mana at times and gotten the lowest level servitor and that caused it to stay around for a very long time, 3 bindings.

>or are there additional factors/possibilities?
>
Both of these can be augmented via edges, although you still have some randomness, and the edges lowered the amount of mana needed to call stronger servitors, when I took them.