To me, that reads like you're using a de facto "zone" system. Which makes perfect sense. I used much the same approach when I used to GM Rolemaster.I also tend to not worry about things to the level of 5' increments, regardless of how the rules are written or the edition we're playing. To me, the various concepts of facing, 5' steps, precising flanking and positioning are all too simulationist / wargamy to bother with. Our group much prefers just getting on with the action and the story rather than measuring out movement on a grid. I still use the various rules for things like disengaging, allies within 5' for sneak attack, etc. We're just not that precise about it, meaning that generally it is assumed that monsters and characters in melee are within 5' of each other and therefor required to disengage if they want to avoid opportunity attacks, and that unless something specific and unusual is going on, the rogue in a grand melee with allies also in melee is going to be able to get sneak damage every round. Accordingly, the mage is also pretty much guaranteed to hit their allies with a fireball cast into melee as well.
For 4e I generally use gridded maps and tokens because I think the forced movement powers in particular, which are such a big part of the system (at least as my group plays it), need this level of precision. One thing I miss with this approach, which I used to enjoy in RM, is being able to make Perception/Observation a bigger part of combat. In my RM games we would often use Perception checks to work out which enemies a given PC was aware of, which meant that having good Perception skills gave a meaningful advantage in combat beyond detecing invisible enemies. In a grid-and-tokens game it is very hard to replicate that sort of thing.
I've extracted what seemed to me the most salient parts of your post. You start by saying you've never had a problem; then you list a whole lot of advice about players and GM discussing back and forth about the details of the ingame fiction; then you state that players have to accept that their PCs will be acting on imperfect information and "need to go with the flow".I've had no problems when I've DMed and with the number of DMs I've played with.
First I would always recommend players to ask questions for more details that would pertain to what they have in mind
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Second recommendation is for the DM to explain details that may hamper their actions before they take them and ask questions in return
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I would take the players at their word that they wanted to move as far into the room as they can while staying out of reach.
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It needs to be understood that a character cannot have a battle awareness to always anticipate whether their planned action can be accomplished or done. Just as in real life a character doesn't have the ability to see the entire field of view from above.
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Players need to go with the flow just as DMs need to go with the flow.
I believe you when you say this works for you. But I find it hard to believe that you can't see how some other players might find the degree of ingame detail "nebulous and vague" - and find the need for player/GM back-and-forth evidence of that vagueness. I also find it hard to believe that you can't see how some other players would find that sometimes, rather than "go with the flow" of what they regard as a bad or unfair call, might try and argue their case with the GM.