The reason that the tails are adzed down is to reduce the size and not create a "point of fracture". That is why it has a curve cut in the bottom.
If you only notch the rafter to fit the step and allow the tail to overhang the side of the plate at nearly full depth you'll have a gap there between the top of the rafter and the top of the plate.
Usually the distance from the top of the plate to the bottom of the sill is a standard board length so that you won't have to buy longer stock and cut of a large piece of waste to make up an odd height of vertical siding.
In the above image the top of the plate is 12' from the bottom of the sill. So 12' vertical siding works great.
And the roof decking is flush with the top of the plate so there is not gap there to fill.
If you raise the rafter you'll create a gap that will have to be filled and fitting boards around the overhanging tail could be a problem.
The tail usually only overhangs maybe a foot or so. And with 2" tongue and groove decking there isn't much load out there that a 2" thick tall couldn't support....
