Similar questions/issues were raised before.
When the main panel displays artists or albums, and you have selected 'show directly under artist or album', the extended panel will expand and display the underlying content in one horizontal bar that you will need to scroll through horizontally.
Far as I know the only way to have the result showing in a 'more generous' grid instead of a horizontal bar is to set preferences globally to 'in a separate panel' instead of 'directly under'.
But that obviously isn't ideal for artists/albums that only have one or very few releases since it will demand more mouse clicks to return to the original view.
Perhaps a request (wish) to have a right click entry on the artist/album that has something like 'expand to new panel' could accommodate for this?
Or, have the extended panel to extend vertically when there are more results than fit a single line.
For as far as I can estimate at the moment, I would support the latter.