Im not sure why this is hard for you to grasp.
Horde respawn 20 at a time at their cave, no one said they respawn 20 at a time from SFGY.
As soon as u cap IBGY, you will lose SFGY, horde attack SHGY. They wont let you keep SFGY while soft capping IBGY.
You cant defend 2 different graveyards, so you either leap frog from SHGY to SFGY or SFGY to IBGY or SHGY to IBGY.
I think here is where you get lost, as soon as you soft cap IBGY, the horde will either send people to retake it or retake SFGY if you have it, because you arent sending 10 people to cap IBGY, you are sending most of your forces.
Even in the best case you hold SFGY and SOFT CAP IBGY, in the 5 minutes for IBGY to turn blue, horde would of been sending people to retake IBGY.
SFGY TO IBGY is 40 seconds and 10 ALLIANCE rez at a time.
CAVE REZ TO IBGY is 20 seconds and it rezās 20 HORDE AT A TIME.
So knowing ALL of this, who is gonna out reinforce IBGY???
Horde send 20 to retake IBGY, your army is already split defending SFGY AND IBGY.
SAY YOU KILL ALL 20 OF THE HORDE at IBGY who are trying to retake it, well they now rez 20 at a time 20 seconds away. Those 20 horde killed 3 Alliance, those 3 Alliance now rez at SFGY 40 seconds away.
So the horde can SEND MORE UNITS AND GET THEM THERE TWICE AS FAST AS ANYWHERE THE ALLIANCE ARE COMING FROM, and its ALL because the cave rez point.
It would be the same scenario if you went to FWGY, they would die near FWGY while Alliance have it soft capped AND THEY WOULD STILL REZ AT THEIR CAVE 20 AT A TIME.
Now in all of these instances remove the cave rez, we would HOLD EVERY SOUTHERN GY WE ASSAULTED NOW.