Custom Expression Easing

I am so stumped with this it's not even funny... Someone so graciously gave me the information in order to get this expression to work:

t = time-inPoint; animIn = framesToTime(6); // 6 frame starting animation animOut = framesToTime(6); // 6 frame ending animation stVal = [10, 10]; // Starting Scale endVal = [-248, -248]; // Calculate ending scale as 10, 10 animEndStrt = outPoint - inPoint - animOut; // Animations sclUp = easeIn(t, 0, animIn, stVal, [258, 258]); sclDn = easeOut(t, animEndStrt, animEndStrt + animOut, [0, 0], endVal); // Combine the animations sclUp + sclDn

My only issue here is I am unable to adjust the ease amounts for the scale property; this is a simple scale in, and scale out animation for subtitles that can be repeated multiple times throughout the project.

scale property keyframes I am trying to use for the expression animation
(Keyframe1: 10 - 6frames - Keyframe2: 258 - end of layer - Keyframe3: 278 - 6 frames - Keyframe 4: 10)

I will normally ease all the way in/out with the graph editor, which gives it the right kind of look. However I am so beyond stumped I cannot figure out how to adjust them in the expression itself/expression graph editor. I really hope I explained it well enough for someone to maybe have an answer, Thanks in advance!