Why does Adobe Sign not allow sender signatures without replacing Signer 1?

When preparing a form that requires signatures, Acrobat allows a signature field participant role to be set as "sender." However, there is no opportunity when sending this form to sign unless the sender adds their email in the "Signer 1" spot on the recipients page when preparing to request signatures. This creates an issue where other signature fields with participant roles set as "Signer 1" are now being assigned to the sender instead of the intended recipient.

I have tried designating the signature fields of the sender to "prefill," but signature fields are not allowed to be prefilled--only text fields can be prefilled.

The only work around I have come up with is designating the sender as signer one and the recipient as signer 2. There are two issues with this. First, when the document has been signed by both sender and recipient, adobe shows that it was signed by three parties: the sender, signer 1 (same as sender), and signer 2 (recipient). This appears strange and unpolished. Second, if I want to send the same document without first signing it, I can't because the recipient then automatically becomes "signer 1" and is assigned to the sender fields rather than the recipient fields.