Because of some peculiar characteristics of the Stickney printing press that was used for B&M stamps, their sheet layouts are a little unusual. The larger stamps (~28x34mm), including this one, were printed in one of four layouts. This stamp (Michel 126) was printed using the most common of the four large-format layouts. I couldn't find a photo of a 126 sheet, but here's a 140 showing the same layout.

It's 100 stamps with 12 blank fields. Your block is from the bottom right of the sheet.