Heres my brief theory take on the big fish, subtle tick thing. I agree with Matt, but have this to add.

A big fish has a huge mouth. When a big fish sucks in a swimbait, its not biting it, its sucking the whole thing in (plus, like Matt said its coming forward). What you feel, the subtle tick, is actually the bait hitting either the roof of the fishs mouth or the back of the throat, or the mouth closing down on your line. Its not like the fish is biting the bait and turning (youd feel a sharp jerk if that happened). Smaller fish cant as easily get a big bait in their mouth so many times I think they actually grab, or bite, a section of the bait and thrash it. Thats why I think most of those harder swimbait bites are from smaller fish. Its more complicated than this of course, but thats my short version.