I'd like to propose we look at this another way. This is not directed to any particular poster so I welcome all responses.
Let's pretend I'm a prospective player to your group. As part of whatever page-setting discussions you conduct, what exactly are you telling me about your table rules regarding what you call "metagaming?" How do you explain what you mean to me, a prospective player?
I once had a thing on metagaming from a prospective player who asked about it.
I’ll come back to that.
What I usually say is, “Anything I say out loud is said to the table at large, even if directed to one person. So if I say it, it’s assumed that your characters keep each other informed at the earliest possible opportunity. I will not rely on your ignorance to challenge you in the game nor try to trick you or trip you up with the rules. If there is anything I want only you to know, I will pass you a note and you’re responsible for what you do with it thereafter, including deciding on sharing the content or not sharing it.
Do not ask any questions while we play. Instead, declare actions that your characters take in the game world to obtain the info you want. If you have questions about the rules or rulings, please wait to ask until after the game. In the moment just tell me what you want to do and how you want to do it and we’ll go from there.
For all actions, please tell me what you want to do and how you go about doing it and then after that, I will tell you whether or not to roll dice. I will also tell you what will happen if you succeed or fail so you can make informed decisions. I will not exploit your ignorance to your disadvantage. Your character has enough training to make an educated guess as to likely outcomes, even if you personally do not. It is okay to change your mind, but please be mindful of the time your turn takes, and consider the other players at the table.”
So the one who asked me about metagaming. It came up in a piracy campaign and she commented that she felt she could trust the other players not to metagame. I took the opportunity to explain that I don’t personally care whether they look in the monster manual, read my adventure notes ahead of time, or try to game me. If they do any of that, they may be cheating themselves out of experiences or avoiding unwanted surprises, but it’s up to them whether or not they want that. My concern isn’t what they think, it’s what they do. How they do, not why they do. So we won’t worry about metagaming in that respect. The challenge in the game isn’t going to be based on a veil of ignorance; it will be based on making hard decisions with trade-offs.
Sure enough, she ended up not caring about metagaming. And sure enough, I’ve had players read monsters’ stat blocks. And it doesn’t matter one bit. Personally, I gain nothing from pretending I don’t know something that I know. And personally I hate exploiting a player’s ignorance to their detriment. It feels unfair to me. As DM I already have so many advantages, I cannot justify making you pretend that fire doesn’t hurt trolls.
Oh! And from time to time, a player mis-hears, or misunderstands (or I’m not clear about) something. When that comes out, I clarify. “Hey, I said X, not Y. You may still think Y, and also Y may be correct to think, but what I said was X, FYI.”
And that’s how I’ve dealt with that at my table. So yeah, the player can tell me where the frog leaps. I don’t care why; it’s not relevant to how I adjudicate the actions in the game.