List of pos_mods for "double" mode:

PM_Same: just as it says, both players start at the same position

PM_Radial   PM_Polar    PM_Right    PM_Inner    PM_LeftRight

  *   *     1-*   *-2               1       2   
  |   |     |       |                \     /
*-1   2-*   *       *   1-*   2-*     *   *     *-1-* *-2-*

*-4   3-*   *       *   4-*   3-*     *   *     *-4-* *-3-*
  |   |     |       |                /     \
  *   *     4-*   *-3               4       3 

PM_Below    PM_Horizontal PM_Vertical

  1   2                   1       2
  |   |                   |       |
  *   *     1-*   *-2     *       *

  4   3     4-*   *-3     *       *
  |   |                   |       |
  *   *                   4       3 

PM_Radial and Polar are equivalent (use -1*pm_radius), so I will
remove one of them soon.