What was Dumbledore's reasoning for placing the Mirror of Erised in a random classroom for most of the year?

Question

The Mirror of Erised was the obstacle that essentially made all the previous obstacles protecting the Philosopher's Stone obsolete.

Dumbledore had enchanted the mirror so that only a person who wanted to find the stone, but not use it, would be able to get it - thus making it impossible for Quirrell/Voldemort to ever get the stone.

However, we know that Harry stumbles upon the mirror sitting in a random classroom when he is wandering around at night under his invisibility cloak. Of course, there is a theory that Harry found the mirror because Dumbledore was intending for Harry to find it as part of a supposed plan to let him "test his strength" and face Voldemort himself.

This theory has its inconsistencies: firstly, how could Dumbledore have predicted that Harry would run into the mirror? He knew Harry was intuitive and he knew he would be wandering around at night with the cloak, but Harry could just as easily not have found it. I think that if Dumbledore had really wanted Harry to know about the mirror, he would have personally, deliberately gone and shown it to him.

We also know that at this point in the year, Quirrell still does not know how to get past Fluffy, so the stone is somewhere in the third floor corridor past Fluffy, it is not in any legitimate danger, and Dumbledore surely knows this too.

This leaves me to believe that Fluffy and the other obstacles are a decoy and the stone is in fact sitting in the mirror in this random classroom. At first this appears to make much sense, but then why does Dumbledore proceed to move the mirror to the third floor corridor a little while later? Does he do that purely to prevent Harry from finding it again?

Dumbledore clearly does not think that Harry would be able to get the stone from the mirror - but of course he does, and in doing so puts the stone in genuine danger for the first and only time. If Dumbledore has a hunch that Harry might go after the stone, why does he risk everything by actually putting the mirror and the stone in the third floor corridor as opposed to moving it to another hiding place that neither Harry nor Quirrell/Voldemort would ever suspect?

Answer 1

This leaves me to believe that Fluffy and the other obstacles are a decoy and the Stone is in fact sitting in the Mirror in this random classroom.

Firstly, I believe at this point, Dumbledore was still making modifications to the mirror to hide the stone. Might be the stone was still on the third floor or Dumbledore had it on his person for that matter. Secondly, chances are that the room Harry stumbles into is the Room of Requirement which presents itself when he's being chased through a narrow corridor.

A door stood ajar to his left. It was his only hope. He squeezed through it, holding his breath, trying not to move it. And to his relief, he managed to get inside the room without their noticing anything.

This theory could be further attested by JKR's description of the Mirror of Erised on Pottermore (now Wizarding World):

Only after Professor Dumbledore makes key modifications to the mirror (which has been languishing in the Room of Requirement for a century or so before he brings it out and puts it to work) does it become a superb hiding place and the final test for the impure of heart.

This still presents some loopholes in the theory. Like this.

how could Dumbledore have predicted that Harry would run into the Mirror?

He couldn't. If anyone knew Dumbledore really well then they will know that he's not someone who does things explicitly. He carefully nudges here and there to get the desired outcome. We've seen his character display this trait in multiple instances.

Harry was being chased by Filch and Snape when he finds the classroom. Snape, as we very well know was a gifted Legilimency user and was hand in glove with Dumbledore. Once Dumbledore had suspected that Harry would prowl the corridors at night he could've asked Snape to corner Harry into that specific corridor. This is evident from Filch's statement

'You asked me to come directly to you, Professor, if anyone was wandering around at night, and somebody's been in the library - Restricted Section.'

After that, they come right at him.