Incorrect icon weight on the right.
Avoid cramming the 128×128 canvas with full-size square graphic. It’ll make your dock feel heavier and not balanced.
What you’ll want to do:
Unbold the icon by resizing it to be slightly smaller. My recommendation is -11 pixel width/height.
May vary depending on graphic weight.
Balanced dock after the resize.
Better comparison example:
Ahh, roomy dock.
Correct weight is what you’ll need to make icon sit comfortably in the dock. Same tip can be applied to circle or diagonal shapes.
Note: In some cases, full 128×128 may be necessary. This is mostly good for icons with heavy transparency (ie: large shadow area, transparency objects, etc.)