Welcome and glad you joined.
Not sure what your asking with respect to RY4?
Are you thinking of adding RY4 along with AT or substituting AT w/ RY4 in the above recipe?
If you are thinking of substituting RY4 for AT, could try using TFA RY4 (Double) at 5% to start.
Not familiar with the AT American Tobacco flavor. Might want to post the blender of flavors in the future.
Could check out this recipe and substitute any tobacco flavor and should work just fine.
re:
Tobacco | Tobacco Recipes