The base is fine as it is. The numbers check for a +6% increase versus an 87% increase, relative to the current rate.
It's like a guy started his job with a salary of $50,000 a year, then after a year got a 5% raise so he was making $52,500. Then after another year his salary was again increased to $56,000. To figure out the percentage of the 2nd raise, figure it out based on the difference between $52,500 and $56,000, NOT the difference between the original $50,000 and $56,000.