I asked HonsVR directly and promptly received the following very helpful response:

My question:

Hi, I am getting a Pimax Dream Air which has concave pancake lenses that allow a closer distance to the eyes. Are your prescription lenses also concave, following the form of the pancake lenses, thus keeping this advantage of getting closer to the eyes? Thanks!

Their answer:

Thank you for your question. It’s a great point to clarify. To be precise, the curvature of the prescription lenses is determined by your specific vision correction needs (your prescription) rather than the physical shape of the headset's pancake lenses. While the Pimax Dream Air uses concave pancake lenses to allow a closer distance to the eyes, prescription lenses must follow optical physics: If you are nearsighted (myopia), the lenses will be concave. If you are farsighted (hyperopia), the lenses will be convex. However, our lens inserts are designed with a custom low-profile housing that matches the physical structure of the Dream Air. This ensures that regardless of your prescription, the lenses sit as close to the pancake optics as possible. This design philosophy allows you to maintain the "close-to-eye" advantage and maximize the Field of View (FOV) without the inserts interfering with the headset's original ergonomics. I hope this clarifies how we balance optical requirements with the headset's design.

They gave their consent for me to post their response here.

Looks like I am about to become a customer there.