To my understanding the way SH4 handles salvos and spreads is exactly how it was on the fleet boats during WW2. They didn't have a salvo tube selection with a gyro offset for the entire salvo like the u-boats did. There was a single gyro offset wheel on the TDC that a crewmember had to change between tubes being fired.

"Fire 1!"
*TDC operator changes gyro offset for tube 2*
"Fire 2!"
*again, TDC operator changes gyro offset for tube 3*
"Fire 3!"

I can't remember exactly where I read this, but I do remember reading that this indeed was a concern with firing torpedoes simultaneously.