When using the lensball you need to shift your way of thinking.

There are two compositions now:

1. Composing the overall photo for your lensball (secondary)
2. Composing the image inside the lensball (primary)

The image around two ball (background now) should not distract from what's inside the ball but should however give enough hint that what's inside the ball is also behind it. You get that by controlling the blur and give the hint by shape or color.

Of course, like any rules in photography, know the rules then break them to fit your style.