A lot of this discussion comes back around to the notion of "DM cheating" which has been argued to death on these forums. Like many things its a spectrum, some players think any DM fudge is grounds for DM expulsion, other people think its find is DMs are adjusting monster stats on the fly as the combat goes on.
At the end of the day, if your group is having a good time....your doing it right.
Back to the OP, I think one of the key 5eisms to remember is that npcs do not have to follow the same rules as PCs, in fact if you look over the npcs in the core books many of them have abilities that are not given to PCs, and there numbers dont' exactly track. So there is never a situation where my player can go "oh well he's a ranger so why are you rolling a d6 instead of a d8?".... I roll the die I roll to implement the game mechanics I want or need to make....and at no point does the player get to know that....unless its a mechanic that would be obvious to the character.
Likewise sometimes I just roll a d20....sometimes its for a random encounter, sometimes its just to freak out my players a little bit and create some ambiance. At no point does a player ever get to "demand" to know what that d20 is for.
Another trick I like to use. Sometimes I will have the entire table roll a check or a save ahead of time....with no knowledge of why. I record the results and use them later. This is great for illusions as an example, the issue always is as soon as the players have to make rolls they smell something is up. But with rolls ahead of time I can describe what they see based on their previous rolls without breaking the immersion. I'm still following the rules, but I manipulate the timing of the rules to better enhance the experience.
At the end of the day, if your group is having a good time....your doing it right.
Back to the OP, I think one of the key 5eisms to remember is that npcs do not have to follow the same rules as PCs, in fact if you look over the npcs in the core books many of them have abilities that are not given to PCs, and there numbers dont' exactly track. So there is never a situation where my player can go "oh well he's a ranger so why are you rolling a d6 instead of a d8?".... I roll the die I roll to implement the game mechanics I want or need to make....and at no point does the player get to know that....unless its a mechanic that would be obvious to the character.
Likewise sometimes I just roll a d20....sometimes its for a random encounter, sometimes its just to freak out my players a little bit and create some ambiance. At no point does a player ever get to "demand" to know what that d20 is for.
Another trick I like to use. Sometimes I will have the entire table roll a check or a save ahead of time....with no knowledge of why. I record the results and use them later. This is great for illusions as an example, the issue always is as soon as the players have to make rolls they smell something is up. But with rolls ahead of time I can describe what they see based on their previous rolls without breaking the immersion. I'm still following the rules, but I manipulate the timing of the rules to better enhance the experience.