Is Polk a heads up specialist? If so that means he likely has a more aggressive style than one might utilize in a 6 max or FR setting. I'm not sure if you're referring to a heads up match (not when it's heads up in a 6 or FR game, but literally 1 on 1 every day) or not.
In any event I see a lot of people overbetting the turn. I notice it a lot more live which is interesting. Some players I've asked say they follow a "make em pay for their draws" mantra so are happy to overbet the turn to get a reckless loose player to chase draws and miss most of the time. A few might say they do it to get better hands to fold or draws from thinking players to fold but that can usually be done with a smaller bet anyways. So basically I think some people overbet the turn to make chasers pay dearly. If you think about it, usually a 3/4 to pot size bet does give poor odds
to chase most draws but it's still like 2:1 which many loose players and rec players happily chase. If you can get a player to call their gutshot with 2:1 odds why not see if you can get them chasing 1:1 or worse!
Another reason to perhaps overbet a pot on the turn is if it's a multiway and there's a lot of draws out there. If you're holding top set on a flush and straight heavy draw board and you have 3 players in it with you and simply bet like 3/4 the pot you risk having them all call you and if anyone has a strong draw they suddenly get better odds. Consider if you have a $40 pot and you bet $30 into it and 2 others call, so now the pot is $130, the 3rd player might be on a nut flush draw and suddenly has 4:1 odds. Make that turn bet $70, the pot is now $110, and one player folds, one calls, the last guy now only has like 2.5:1 to call.
My numbers might be a little off but in general overbetting the turn gets fish to pay dearly for draws, and to weed out limpers in multi way draw heavy pots.
They don't always have the nuts either when they're the ones shoving the turn , I've called down people before who spew shove the turn on draws or spew shove with 2P on a paired board and lose to a set, turned straight, or better.
If you have the nuts you want value. You really have to know your villain to know if a value over bet is needed. If the villain thinks they have the best hand (like 2nd nuts to you) they may insta call. If they think you're a bluff machine they may see you as stealing and call with worse.