A defining feature of sensory data is that we can sense it.
We are free to propose any number of non-sensing ideas that we like. Euclidean Geometry, Integers, electrons, circles,.... But only those things we can sense have any significance for us.
We have no direct way of knowing the charge on an electron. The only information we have is the relationships. Our only knowledge of integers comes from our relationship with those ideas.
In order for sensory data to be sensory data it must be possible to have a relationship with that data. And the only thing we can sense - are relationships.
Anything that isn't a relationship is irrelevant.