The draw-bridges in the structure are at the top of the walls, and allow access from the inside wall to the outside wall. I tried to have straight walls between the towers to have the fastest route available to move from one front to another. If you do not want to guard the drawbridge, then raise it, you cannot bring people in from the outer wall while it is raised but that is the price that you pay...
In theory, if the walls are breached at ground-level, then anyone entering will be surrounded, and it will be very difficult to completely depopulate the outer wall due to the inner-half of the diamond-shaped sections, which should be covered by the outer-half. If the outer wall is taken, then raise the draw-bridge and harass them from the inner wall(which should be slightly raised) and the towers(whose main purpose is to harass the outer wall. After being inspired by that article, I would suggest increasing the size of the diamond-shaped sections so that they extend beyond the wall and allow vision of the wall between them.
Note that this is D&D, not DF, an impact is less likely to model the mass and velocity of the projectile and apply a deflection modifier which degrades as it is deformed by multiple blows and more likely to deal fixed damage to a wall based upon the weapon used to launch it. So the angled walls here are less about mitigating damage and more about confusing people as to exactly where to teleport to and making it difficult to get close enough to use lower-level effects. For example, spider-climbing up the walls would require scaling the heavily-defended diamond section, or walking past it and hoping nobody there is looking.