Using a calculated lead angle and firing the torpedo on 0deg gyro is no longer possible after you get the passive skill for your torpedo man that increases the damage and
speed.
Since the torpedoes are actually travelling faster than you think, they all go in front. Nowhere does it say what the actual speed is; even after spending 5 points to max out the skill, G7e is still listed at 28kts.
Had me scratching my head as well when I tried adopting my familiar tactics from SH4.
Possible that the TDC doesn't take the new speed into the calculation either btw, though that 'TDC off' method with lining up the numbers still gives good accuracy.

(always relatively short range though)