[TowerTalk] Which better: TOP of hill or SIDE of hill?

[John WA2GO]

My new qth-to-be has a north-south ridgeline running through the center of 
the property.
I can put towers right on the ridgeline at 600' ASL, or I can put towers 
down the sides of each hill. In the latter case, I would have an 
Europe/Africa/S. America at 550' with 50' of hill rising behind it, and a 
US/Asia/Oceania/S. America tower at 530' on the West side, with 70' of hill 
rising behind it.
(This setup also puts the East and West towers 700' apart!)

Question is: Which is best?
  a) being on the hilltop,
  b) being on the precipice of the drop-off, or
  c) being partway down a 250' slope, with 50' - 70' of hill sloping up 
behind the tower.

(Yes, it slopes down 250' to both East and West, as well as North!!)

I would experiment with dipoles, but I can't really experiment now, because 
I don't own the property yet.  Also, I imagine the answer might be different 
for 40M vs. 10M.  I can have a single tower for each band if necessary/best.

I am in the permitting process, and I want to apply for what I really need 
in order to maximize my chances for approval.

Is there modeling software I can use that takes into account the terrain 
BEHIND the beam?  If so, which one?  Anybody out there already done this 
modeling, or better yet, already done real-world experimentation?   
Intuition says having slope up behind beam is good, but that's only 
intuition. Wondering if it is, how much slope is needed in order to be 
worthwhile, on each band.

Thanks!

John
WA2GO