One other thing people are forgeting is the position of your seat belts in relation to your shoulders. For hans to work and be comfortable the shoulder fixings should be as close to level as possible, if not the hans will not only be very uncomfortable but could also brake your collar bone in a crash..I belive more instructions are on the Hans sites..
Except Stand 21's HANS instructions tell you to have the belts 10 - 20 degrees below a horizontal line, and if you mount them above the horizontal then it's incorrect. The Blue book says 10 degrees below or above the horizontal is preferred....!! The MSA's drawing for the preferred angle of the belts in the horizontal plane is also completely opposite & termed incorrect by Stand 21!! We spent a fair bit of effort setting up the belts just as the MSA 'prefer'...!! 
I also read somewhere that it's recommended that for HANS use your shoulder belts should be crossed, something I'd also been told years ago & had always done in my rally cars 'back in the day'. However when my son & I turned up for our first hillclimb with the belts crossed, the scrute wouldn't let us run until we uncrossed them....!!
I can see mass confusion reigning next year...
