The Collision Area and Hitbox are kept separate because the level of detail required for an event can vary significantly. Now, let’s move on to the setup steps.
"How do I change it for an event?"
Some people like it big while some like it small, simply add this comment to the event you want to change size. Note: Comment (green text), not Notetag
<collisionRect: width, height, offset X, offset Y> (all in tile unit but support pixel)e.g. <collisionRect: 1.2, 1.2, 0, 0>, <collisionRect: 5, 5, 1, 2>
From the example above, 1.2 width height = your game tile size, by default should be 48, but with addition of .2 of that tile size.
To see the visual for debug, please press the button you assigned in plugin parameter which to show collision area. The collision area will display in green.
"Changing size makes my event sprite not centered to the new collision size!"
I think this picture should explain how you do that easily enough. Red dot is your event sprite.