I have decided to make changes for this rule in the player’s handbook.
On page 10, left hand column, there is a chart I am modifying for my game world.
Int 15-16 70%, 14 to 22
Int 17       80%  16 to 24
Int 18      90%   18 to 36
Int 19      97%    20 to all
These are spell book amounts. The spells per day is a separate chart in this blog.