The round layout requires at least 8 bubbles for the center bubble to appear bigger than the rest (otherwise there aren’t enough other bubbles to form a complete circle around the center one).
The Off-center layout offers an alternative for smaller clouds, where the outer bubbles don’t necessarily form a complete circle:
Once you have enough bubbles in the cloud for the center bubble to separate from the rest, you can control the order of the bubbles via their weights: the highest weight bubble will appear in the center, and the smaller weights follow in clockwise order:
Tap the pencil (or double tap an empty area of the widget if you hid the pencil) to enter cloud edit mode. Tap bubbles to edit their weight:
Lock the bubble sizes in the cloud configuration screen so they don’t automatically update based on use frequency (bubble weights are shown in cloud edit mode, only if bubbles sizes are locked):
To enter the Cloud Configuration Screen press the ⊕ in the toolbar (or triple tap an empty area of the widget)
More information about the new layouts: Version 9.72: Layout options for home screen widgets
Thank you to KL for the question prompting this post.