I am in complete agreement with what you said that I need only talk about reality to have something to check my map against.

But I believe we may be using the term "epistemic possibility" differently.

It appears to me that when you say that X is epistemically possible, that it is possible that your map can contain X (and your map is correct in this aspect). I.e. that one can have a true belief that X.

What I mean when I say that X is epistemically possible is that I have a justified true belief that X. In that sense epistemic possibility is stronger than metaphysical possibility for me in that I require the justification of the belief as well as its truth.