Nikon F4 and SB 21.

Simple enough question The above combo to work in TTL. Set camera to A and flash to TTL. I normally use spot but this would be better in matrix?

I believe what mode you set is irrelevant when using flash, as that is only measuring ambient. And in A mode the shutter is automatically set to the highest sync speed. (1/250 on an F4) It takes its reading off the TTL sensor below the mirror. It uses the focus point, not the metering mode. I don't believe a SB-21B has a balanced fill flash setting and I know it has no preflash, as it is not i-TTL. You would have to set the camera to manual and lower the shutter speed to balance any ambient light.