Anyone know if the 9% bottom tier support mastery multiplies the ambient mana regen increase, or if it only applies to runes/masteries/items?
I'm gonna try and experiment a few games, but I figured it would be cool if someone knew for certain already.

no idea, id love to know this as well

I think it does actually.
I played one with no 9% mastery and my mana regen at lv 12 was 40. I played another game where the only thing I changed (including what items I had at level 12) was adding the 9% mastery and my mana regen at level 12 was 53.
40x0.09= 3.6.
53 is a lot more than 43.6.
Without the 9% mastery my mana regen was 53 at level 18.
With the 9% mastery it was 53 at level 12.
I didn't make it to level 18 on my 2nd game, so I dunno what it was at lv 18 with the mastery, so I'm gonna have to do more games till I can get that number, but as of now I think the mastery applies to the ambient crystal scar regen buff. ;oD

So just did another game, and the # kept changing for some reason. I didn't see anyone with aura items, so I'm guessing that there might be a bug with what the character stat screen shows. The #s looked right as I was leveling up, but once I hit 18 it kept changing almost every time I opened the page. Oh well.

Is that how it works? Makes sense.