Is the sentence intensive or reflexive you set it by itself on the shelf?

'You set it by itself on the shelf.' is a reflexive pronoun, the object of the preposition 'by'.

The intensive use usually places the reflexive pronoun immediately following the noun antecedent. For example:

You, yourself, set it on the shelf.

The sentence would need to be reWorded to include the antecedent noun for the intensive use of the reflexive pronoun; for example:

The book, itself, lay on the shelf.

Note: The book, itself, can't set itself on the shelf, someone has to do that.