I'm no expert... had to get that out of the way first. On the Sterlings, there are several coils to the rear of the receiver that have nothing behind/inside them (meaning "exposed"), then there are a few coils of the spring that go over the end of the bolt, so they aren't "technically" exposed. If say, three coils are over the bolt and the other nine coils are beind the bolt in the receiver (exposed)... wouldn't you be good?
Edit: For example: On this Sterling, there are eight coils "exposed" and two coils over the bolt. Depending on how you rotate the spring, you should get the desired number of coils "exposed". Unless, you got a different spring other than the standard... then you may have to cut coils.