So this is how I see it. Usual caveat, probably others will see it differently and everyone can enjoy their games nonetheless.
I guess my primary concern is how to target your spell. Obviously you have to target the chain. But then how does the chain know who to wrap up for you? You could enchant the chain, and then probably be able to direct it against a specific person, but that's not what we're doing here.
If you'll indulge me for a moment, let's have a look at two core spells similar to your proposed Chain the Unwilling Enemy, and see how they deal with targets etc.
Weaver's Trap of Webs, ArM5 p117.
CrAn 35: Base 5, +2 Voice, +2 Sun, +2 Group.
Coils of the Entangling Plants, ArM5 p138.
ReHe 20: Base 3, +2 Voice, +1 Conc, +2 Group.
Coils of the Entangling Plants manipulates plants already nearby (in a very specific meaning of nearby) and grows the plants in a particular way through the space. If there is no-one there the spell works just fine, maybe its useful to cast nonetheless to form some sort of porous obstacle. If one or several people are in the spell area, they get entangled, but that's not because of any targetting onto those people.
Weaver's Trap works the same way, except it creates webs rather than using existing ones. If you are in the way of the webs, they won't target you directly. They just do their thing.
The Form-stuff just doing its thing, it seems to me, is how come Parma can be slipped past in these cases.
So, Chain the Unwilling Enemy. Do you want the effect of chains filling a space to chain anyone who is there, or are you more interested in the 'directed control of the chain' concept?
Because if the latter I think you should look at magic items/a talisman.
If the former probably a CrTe version of Weaver's Webs will work for you.
Although you should be wary of the Terram base item being a cubic foot of metal, whereas the Animal base item is a pony. Which seems to be about 17.5 cubic feet? Not sure there is consensus on that. So you probably have to add some size to the CrTe chains version. Maybe.