The easiest way I can think of is to skip that tool completely, because it's basically designed to do all the complicated changes to make the motion look more "natural."
Simply open the clip in the PiP Designer and use the keyframes to set the start and end points. The motion will be completely linear, and you can still check the ease-in and ease-out boxes if you'd like to gradually ramp the speed up at the beginning and/or end of the movement.
There are lots of tutorials on keyframes if you need any guidance.
YouTube/optodata
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