I don't think it's a state secret though. It's not alchemy. The Dolphins have $81.8 million worth of salary cap figures on contract for 2013. That much is known. The unknown is how much the salary cap will be next year. This year it was $121 million (actually I think something like $120.6) and last year it was almost literally the exact same. An increase is not really forecast for 2013, or if you do see an increase it will be a modest one. The big increase should come in 2014, and you see that already baked into some contracts (Rob Gronkowski's being a good example).
The Dolphins' adjusted salary cap this year is $131.0 million and that comes straight from the NFL. As of September 7th, again per the NFL themselves, the Dolphins were $4.0 million underneath that salary cap. That gives them the ability to roll whatever is left of that $4 million after the signing of Jabbar Gaffney (probably all of it, doubt they paid him more than Naanee) forward to next year.
So let's pretend the 2013 cap doesn't grow, just like the 2012 cap didn't grow. Let's set it at $120.6 million. The Dolphins get a $4.0 million rollover credit and it's now $124.6 million. They have $81.8 million in cap figures under contract. That means they have $42.8 million available. If the salary cap does grow in 2013 I can just about guarantee (based on the economics) that it'll be a maximum of about 2 percent. So let's add $2.4 million to that. These wide estimates ($40 million to $65 million) really are unnecessary because the actual highway is about as wide as $42 million to $45 million, barring any further signings. Performance bonuses will change that a little, but not much.
Based on that, and the fact that the rookies will cost $6 million, I really don't believe the Dolphins have the room to do much more than re-sign their own guys. Even discounting their 1st years will only just barely keep you under the cap when you consider the $6 million for rookies.
If the Dolphins are going to do anything in free agency it will be at the expense of a player or players currently under contract (Dansby?) or at the expense of a pending free agent that they choose not to keep (Fasano?).