What has dosing of rHGH to do with exogenous insulin?
They have an extremely high synergy when using decent amount of rHGH jointly, but the way you react/cover to exogenous insulin depends(aside of your insulin sensitivity) mainly of your carb intake(as well as fats and proteins, that is another of the reasons you avoid fats when using fast insulin, not only because you do not want them to be forced in as nutrients priorizing carbs and protein but a delayed peak for insulin).
You make your maths regarding insulin based principally/almost only in your carb intake, and secondary protein. There are recommended ratios for rHGH/insulin to get the best of them jointly, but in any case a 20% is going to make any difference regarding that ratio, even because those "ratios" are very questionable and there is nothing confirmed.