In the folder for your warfare mission, there is a file called, init_common.sqf, open it with notepad, then add this line...
BIS_WF_Common SetVariable ["sidePlacement",[false,-1,-1]]
This tells the game not to randomize the starting locations. It should work after adding that line.
Also, startinglocation0 will be the starting location for the west faction, startinglocation1 will be for the Opfor and startinglocation2 will be for resistance.
that sandbox.darrenbrant site is quite good, download one of the custom missions on there and reverse engineer it for more info.