Here's a Billy Buff suggestion; increase the maximum speed of the projectile. Maybe quite significantly.
The increase in usefulness is two-fold:
targeting will be easier. Instead of reducing the damage fall-off, or increasing the max-damage radius, just make it a bit easier to put a missile where you want it.
a quicker projectile will spend less time within the firing radius of TMD. If not passing directly through the centre, a faster projectile might have a better chance of passing two TMD's with some health remaining.