Tables are inherently hard to make responsive.
Yours is actually pretty good, the reason it stops scaling too early is because of
directors/officers/members
Which is unable to break into several lines. Replace the slashes by spaces and all is well.
When the table is styled properly with % width like yours, the one thing that will stop a column from shrinking is when the text inside cant be broken out.
There may be additional CSS that could allow the line to break, but you will have to research that.
Note: You are using Smart Mobile mode (that gives the Fullview icon), this is really an old deprecated mode, and you would be better off using a responsive mode