Movie Title Styled String
JavaScript (ES6), 86 82 81 80 bytes
Input is expected in currying syntax f(s)(r), with:

s = string
r = ratio + direction: a negative float for inward or a positive float for outward



let f =

s=&gt;r=&gt;s.replace(/./g,(c,i)=&gt;c+' '.repeat(n+=i&lt;l?-r:r),l=s.length/2,n=r&gt;0&amp;&amp;l*r+r)

console.log(f("INTERSTELLAR")(-1));
console.log(f("INTERSTELLAR")(-0.5));
console.log(f("CODEGOLF")(2));
console.log(f("CODEGOLF")(0.4));