Target N1 vs thrust relationship

[alosaurus]

I know it is not linear,and the majority of thrust is available at the higher values,but is there an easy way to work this out(or some noddy rule of thumb).My aircraft has RR A3007/a engines(sea level flat rate of 14,850 lbs thrust).If the difference between max t/o and restricted t/o thrust is 3.2% how much thrust does the restricted t/o lose (87.0% vs 83.8%).