If you wish to use Homasote on the elevated portion:
Once you have established the smooth vertical curve transition into the incline then you can terminate that piece of plywood and continue with incline plywood by lowering the incline plywood 1/2" and back it up 8" +/- and attach the top of the elevated plywood to the bottom of the transition piece. This gives you a 1/2" step to continue with Homasote for the remainder of the elevated portion.
For purposes of this paragraph let's just imagine the dual track subroadbed is 9" wide. When you have already cut your subroadbed material and it is on a curve where backing it up would not be work well then simply fabricate a matching curved 9" X 16" gusset attaching it 8" (half way) under the severed incline, add a 9" X 8" piece of curved plywood on top of the exposed portion of scabbed gusset as a extension of the established incline. Now that 9" X 8" add-on-piece becomes the sandwich interface for the bottom of the vertical curve transition piece. With that done you have a 1/2" step down and to accommodate the 1/2" Homasote and can now continue on up the hill with Homasote.
Once you work with Homasote it is hard to go back to laying right a way on plywood decking.
Continuing: if dropping the rest of the 1/2" plywood ramp happens to mess with your calculated clearance for the lower tracks which you are going to pass over, no problem. Just use the step method again. Stop the plywood 4" back from the C/L of the lower track, stop the Homasote 12" back from the C/L of the lower track, and instead of using Homasote use the 1/2" plywood as a replacement for just over the lower track. This will recapture the clearance you originally desired. Now once past the lower track reverse the step to return to a Homasote working surface.
Over pass Homasote substitution example:
Because of the shallow angle of the overpass the 1/2" Homasote replacement is quite long. The brown paint is where the Homasote stops. The plywood is the same stiff 1/2" Birch multiply we used on GRJ's main decking.
This view shows how long the top plywood gusset had to run. The spiral easement template is to draw a centerline for the track.
The intrusive block corner is now embraced with a light weight removable mountain so as to be able to easily service the turnout
