far, distant, remote, slight
邈 centers on great distance: something far away, remote, or faintly perceptible. The 'slight' sense extends this idea to something so distant it is barely noticeable.
邈 combines 辶 (movement) with 貌, which likely contributes the sound and the idea of something distant or faint. The exact historical development is uncertain.
The movement radical 辶 surrounds 貌, which looks like a face or appearance. Imagine a face so far away you can barely make out its features: that distant, slight image is 邈.
For バク, picture a distant figure waving a backpack: backpack -> バク, and the figure is so far away it's barely a speck.