ok, found this. It looks like the cut off is at the luxury tax line:
Cap Exceptions
Old Deal: Every team received a Mid-Level Exception every year (up to five years starting at $5.8 million last year) and a Bi-Annual Exception (up to two years starting at $2.1 million last year) every other year.
New Deal: The MLE is now four years and will start at $5 million. Teams near or over the luxury tax line will be limited in the amount they can spend, being restricted to only adding a MLE deal up to $74 million in total salary (in the first year). A team with $69.5 million in commitments, for example, is limited to $4.5 million for the MLE. Teams over that amount can offer a mini MLE of three years starting at $3 million. The Bi-Annual Exception remains. A new exception worth $2.5 million is available to teams who use all their cap space to sign free agents.
The Players wanted the MLE to remain unchanged for luxury tax teams. However, from the Owners original demands of no ability to use the MLE for tax teams as well as wanting to restrict the length of the deals to alternating between three and four years each season at their last offer, it’s a win for the Players. Scaling the tax starting at $69 million in cap commitments from $5 million down to $3 million was an excellent idea and means teams with a lot of committed money can still add a free agent. Call the new exception the Miami Exception.