I have been playing my recent games with this new optional rule I have come up with. I present it here for other players to use in their game if both players agree to it. You will have to make up markers for it.
Only non-machine figures can go prone. It costs 1 MP for a figure to go prone. Place a Prone marker next to the figure. Getting up from prone can only be performed if Walking speed is chosen. If 1 MP is spent, the figure is marked as kneeling. If 2 MPs are spent, remove the prone marker and they are standing. Kneeling and Standing figures can fire through a prone figure with no fire DRM. If fired at, the prone figure gets a -1 DRM. A Prone figure receives no benefit against a grenade attack. A prone figure that walks can move 1 square forward or directly to the side. A prone figure can run and move 2 squares forward or to the side OR 1 square diagonally. A friendly figure can walk through (but not end movement in the same square as a prone figure. It costs the moving figure +1 MP to do this and can only be performed when walking. Enemy units attacking the prone unit in HTH combat get a +3 DRM.