POLL QUESTION: Ghost Star vs Undrastormur

Both the Kindle and paperback versions of Ghost Star are coming out on 01/09/18. The second Undrastormur book (Kindle) is ready to go now. Should I publish the Undrastormur book BEFORE or AFTER Ghost Star's release? 

I guess I'm concerned about the two books possibly getting in each other's way. Am I overthinking it? 

Feedback appreciated.