What is the comparative form of in?

The word "in" is a preposition, and prepositions don't have comparative forms. Comparative forms are used to compare two things, like "bigger" or "faster."

If you're looking for a way to express a relative position, you might use words like:

* More deeply: "The cat is more deeply in the box than the ball."

* Further inside: "The book is further inside the shelf than the pen."

* Closer to: "The chair is closer to the wall than the table."

The specific word you choose will depend on the context and what you're trying to convey.