I bought a Mugen Max (serious overkill, but price was good) for my long-overdue new build. Some sites list 1151 for it, and some don't, and I've seen several mentions that 1150 and 1151 are the same as far as coolers go. But I've also found mentions that it's not compatible with 1151 without some extra spacers that have been added to newer units.
I tried sending emails to support, but the US one came back undeliverable.
UPDATE: I had previously written that the email to EU support hadn't gotten a response all week, but I later discovered that they had, in fact, responded promptly but fell victim to an overly-aggressive spam filter.
Given the information in the posts below, I still think it's prudent to avoid tightening the screws until they bottom out, but there's the official response.Socket 1151 is identical with sockets 1155, 1156, 1150. You can use the instruction of 1155/1156 for socket 1151.
Please don't hesitate to contact me if you have any questions or require further information.