I think when you do that you denied having premium hands
With AA/KK and even QQ you would have certainly 3bet 2.5x or 3x.
You can also maybe add AKs or even JJ depending on the reg profile.

I think the reg knows it, and he can set up his call in accordance (BTW we need to know how many BB he has).

There is also 7 players to talk behind you.
If the reg would have been CO and you D it would have been different because his range would be wayyyy looser.

My play would be a mix between :
- 3bet 2.5x
- call

Ok we need to be aggressive at that level, but 20BB could still play and we do not have the best position at the table...

With 20BB from these positions I would not have a non-AI 3betting range. The range we play is so narrow and amount of hands that profit from non-AI 3betting vs the other 2 options so small (KK+ namely), that splitting our range her like this does not make much sense. Calling and jamming are both fine, depends mainly on your opponents opening stats and also a bit on the stacks and players behind.
When you think that the other players (esp the opener) are better than you, that would also sway me towards jamming.

ATRC I don’t think having a 3bet range of 20bb is generally really good especially for ep vs ep you could maybe use this a an exploit in the micros and only 3bet top range for 2,5x. And even in micros I would never use 99 as a 3bet you going to narrow the utg range too much to call a shove + playing post flop will get awkward a lot with this stack size. I think Ev between shoving and calling are really similar so you could go ether way IMO. I would base my decision on the read I have on utg (If he seems to tight I would mostly call/too loose shove)

I don't mind having 3bet or flatting ranges if you are masterful enough to be precise with narrow ranges. That being said, 99 is not your hyperpolarized 3betting hand nor does it love taking flops at this stack depth, this is not a set-mining stackdepth and youll basically be crying on most flops. It's a pure jam.

Against wide openers it is a jam and against tight openers is a right away fold. May choose to shove as a bluff AQs instead of 99 since it has more equity when called and gets called less often due to blockers.