Thanks for help

The height, proportions, etc, of a Shelf is theme related.

So, you can either use a different theme OR you can try increasing the scale (right click on the Shelf's left mini-tab -> Appearance and Sounds -> Scale).

you can also double click a tab that has more icons than show in a row to show them all, but don't know how long that persists

The number of rows (or columns, in the case of a vertical shelf) can also be specified in the shelf's 'Shelf Properties', if memory serves.

However, essentially, the height (or width if vertical) of a shelf, as Jorge already said, is largely determined by the theme. Now, while an experienced 'themer' would have little difficulty changing/adjusting shelf dimensions, it's not something I would recommend ordinary users to even try.

To manually increase the number of visible rows you can also left click on a tab (while the Shelf is open/expanded!) and drag it up.