Getting Started - Send for Signing Question

I'm working my way through the API Getting Started guide and have managed to successfully authenticate via the API and upload a PDF file, create an agreement and send that to a single recipient.

Just looking to clarify when you just upload a PDF here and specify the recipient/s what rules does Adobe Sign use here to determine where to place the signature field on the PDF on the signing page? Does it look for some blank space and just add this to the first available blank space it finds on the document?

In my tests with a few different PDF files it is creating a 2nd page to capture the signature for one file, but on another it simply positions the signature field on the first page of a document which has lots of blank space.