In Chris Voss’ negotiations book: Never Split the Difference…

In Chris Voss’ negotiations book: Never Split the Difference, one of the tips is: “Prepare an Ackerman Plan.” This is an offer–counter offer model to help you structure what type of offers you are going to make, until you arrive at your final price.  First, determine the final amount you are willing to pay. Then, Step 1: Make an offer of 65% of the full amount you are willing to pay. Step 2: If that amount is not accepted, your second offer is 85% of the full amount you are willing to pay. Step 3: If that amount is not accepted again, your third offer should be __% of the full amount you are willing to pay. Step 4: If that amount is not accepted yet again, your fourth offer should be your final offer of 100% of the full amount you are willing to pay. What percentage should your third offer be, of the full amount you are willing to pay, in Step 3 above?