Interdictors ?

Recently I thought up a "new" system for use in Full Thrust....As I'm
new to this list I hope this hasn't been discussed too much already.

Gravity Well Projecters (no points for guessing where the idea came
from)
They come in a light and heavy variant.
One arc only.
The light takes 20 mass with a 1.5x mass in point cost.
The heavy takes 30 mass with a 1.5x mass in point cost
The range is approx 40% and approx 60% of the playing area respectively.

They can only be mounted on ships with a minimum mass of 100 and they
have effect within the entire area they have range to, i.e. they are
effective within their 60 degress cone up to their range. The effect is
simply to make FTL drives useless within the area. (Regardless of who's
FTL drives)

I thought this would be a nice system to use in a campaign game, where
forcing your adversary to stay and fight in a bad odds battle would be
very nice, though you would have to pay around 350 points for it (a NAC
Victoria without the Torp's, class 3 and 2 batteries and 2 FC). They are
supposedly easy to make, hence the low cost but just take an awful lot
of mass. I beleive this would be an option which wouldn't in any way
unbalance the game, but would rather add an extra layer of debth (though
still in campaign mode...) What does the list think ?

Sindre