Does it matter if the book is a Paperback or Hardcover?
Yes and No
I can work on both formats, so neither have qualities that prevent me from working on the edges (unless the book has deckled edges of course)
However, some designs can be a bit stubborn, and the flatter the surface (eg no hardcover cardboard in the way), the better. But by no means does the hardcover cover prevent me from adding edges to a hardcover book. The biggest difference on the way the cardboard can change the edges is probably a split stencil design over a series. The cover creates seperation between the books and can cut up the design a bit, while paperbacks can be sprayed without any interruption, that can make the design pretty seamless
So the only way the format matters is in the sense of making my job a bit easier, and designs more seamless when spread over several books