I've dealt with this a few times. Canadian Codes are a bit different, but the way I've dealt with this is that (a) the initial point of bearing must be full width, ie: the birdsmouth doesn't start until the top plate; and if this is not the case then (b) if the birdsmouth begins before the top plate, I'll take the width of the rafter at the point it starts at the top plate and calculate for a contiguous rafter of that size.
In other words, if you hack a 2x6 down to 2x4 size at the start of the top plate then I'll calculate a snow load based on a 2x4 throughout.
Two ancillary thoughts: most old-school carpenters don't goof on rafters, because they were taught right and know what they are doing.
My concern with with the original post is that the lintel bearing the weight of the rafters appears unsupported.