Why do we say
Could you please put it on the rack above you?
In other words, why is there no reflexive needed here?
Can we also say "above yourself”, that is, use a reflexive pronoun?
Could you take a picture of yourself?
Could you put it on the rack above you?
These two sentences are imperatives. Imperatives usually do not take an expressed subject. Instead they have an unexpressed subject, you.
In example (1) above, we see that if a pronoun later in the sentence refers to the same person as the unexpressed you, then we need to use a reflexive pronoun.
Why then, we might ask, does the Original Poster not need a reflexive in their example, (2)?
The reason is that this rule does not apply if the pronoun occurs in a locative adjunct. A locative adjunct is just a phrase that gives us extra information about something, specifically by telling is about its position, direction or location.
We can see this contrast in the following two examples:
Here we see two preposition phrases with the preposition by. In the first sentence it is being used to give the location of the man, and therefore no reflexive is used. However, in the second sentence the word by does not have a locative meaning and so we have to use a reflexive.
In the Original Poster's example, the pronoun you occurs in the phrase above you, which tells us about the location of the rack. For this reason no reflexive pronoun is needed here either.
Not really, because "above you" describes the rack, and the rack and "you" are not the same, so a reflexive pronoun is not appropriate.