They never actually state where the aft Phasers are on the ship but over the hangar bay doors would make sense as this would give better than 270 Degrees lateral and 120 Degrees vertical.
Actually in TMP the Enterprise has maximum firepower when in top view maximum aspect to the target as all Phasers can fire at the target, which would be above the ship. One reason why SFC should have been in 3D!!
Stephen V. Cole went through every TOS episode with a fine toothed comb for SFB and managed to cover all weapons and operating systems in the game. THe 6 shields from "Elan of Troyus", Klingon Drones from "Errand of Mercy", Plasma Torpedo from "Balance of Terror" and countless other tiny details that made SFB as true to TOS as it could be, and now we have SFC.
A lot of the gaps left by the writers of TOS had to be covered, even TOS has incosistncies, vaguries and contradictions.
The SFB game had a "feel" to it and that transfered into SFC as well.
Do you thnk that this forum would exist if it didn't. Not that many 9 year old games have such a large fanbase and active participation, third party patches, thrid party enhancement and supprt software, a vast library of models that grow day by day, etc.
Franz Joseph filled a void and Stephen V. Cole filled a hunger to play at starship captains and pit our wits against various enemies (other players) using cunning and wits, just like James T. Kirk.
At least, with SFC, a game doesn't take all day now.