The actual distillate in the base gasoline is a big determining factor of what an octane booster will do. Gasoline is a hodgepodge of distillates that a refinery throws together to make max product for the least money. As long as it meets requirements (octane, vapor pressure etc) then it is good to go.
Going back to lead, some distillates are really sensitive to lead (triptane) and show a big octane boost when lead is added. Some distillates, not so much. There was a lot of research on this during WWII by the Army Air Force to find fuels that would power their new high compression/turbo/supercharged aircraft engines.
I believe some stations now only buy regular and super, and mix them at the dispenser for mid grade product. It is close to linear, as far as octane ratings go on pump gas. When you start mixing leaded racing gas into your regular no lead fuel, then the math goes out the window. It is a huge variable there.