My hunch is "solid" for the 8/16 level is "doesn't open limp, raises what can be considered an appropriate range of hands from EP, but may miss value post, and also likes to 4 bet pre with solely the top of his range".
So on that token, I remove AA, KK, QQ from his range. I'll also remove AKs from his range. So we're probably talking a range of 88-JJ, AJs, AQs, KQs, AKo, AQo preflop.
Of these, I think he'd raise his AK on the flop, as he'll understand that it's a good hand, but be worried his KQs has "kicker problems" and play it more passively.
I do give him 88 in his flop check call range, since expert slowplay is common at this stake level.
So really, we're left with this once he calls flop:
Losing to - 88 (3), KQs (3)
Beating - everything else
This is obviously a rosy scenario as we can't be assured he 4 bets hands pre, nor that he's that ABC on the flop in narrow range 3 bet pots, but I don't think it's a bad approximation.
OTOH, I think the cold caller is way more likely to be the one w/ the King here. Hands like K7s are like prototypical "fish cold call" hands that they'll want to see a flop at any price with, but then play station-y without at least two pair. This being said, because he's so loose, he's basically as likely to have the 8 as he is the King in this spot, and can have all sorts of stuff that will just call down (like when you think a fish won't call the turn and river w/ 55, be advised that they will, and they do, even on like a river 7
sometimes, because "the Ace didn't come"). And you have to discount a King at least somewhat, because even a passive fish knows top pair is a good hand and might do some passive fish w/ a good hand thing and donk the flop, or check call / donk the turn.
Really I think UTG has 99-JJ here a ton, and fish has...well,something. So we should bet.