The bubble “weight” value controls the size. It used to be called “bubble size”, but in some layouts the bubbles actually have the same size, and the weight controls their order, for example:
To modify a bubble’s weight, open the folder from the app drawer, then long press the bubbles, and use the + – on the left and right of the app icon:
The actual weight value is shown next to the ruler below the app icon (“📐1”).
Generally if a layout has different size bubbles, the higher the weight the bigger the bubble. In layouts with same size bubbles the “heavier” bubbles sink lower.
Important: long presses are not detected in the tile! (WearOS captures long presses and takes you to the tile management mode). So you have to open the app drawer, then the folder which is assigned to the tile, and long press bubbles in the folder.