I am convinced that the angle setting for Multi-Monitor is completely non-functional and always configures the screens to be 45 deg. from the center screen i.e. 90 for the parameter value.
This happened on GT5 as well, it's just taken me years to figure out what is wrong.
One of the best ways to test this is to observe the staging camera view at brands hatch. (when you are in the event but before you start the race) The view there makes is particularly noticeable if your physical screen positioning is deviating, because it is looking down the pit lane with a lot of vertical geometry to the immediate right and left.
I personally have my screens at about 65 degrees each from the center screen, which should mean the setting should look correct at 130.
However, when I set it to 130, the projection of the side screens is canted inward, which is consistent with the actual utilized value being about 90.
What's more, no matter what value I use, the projection always looks the same.
The only other possibility I can think of is that perhaps the parameter is only broken when the client PS3s are set to use the server's settings, that's how I am configured right now.
I'd like to hear some other opinions about this.