xfce4-panel v.4.9.0+ has a new vertical mode (deskbar) and multiple rows layout. At the moment xfce4-dict panel plugin does not use these features, for example the icon size is always equal to the panel size regardless of the number of rows.
Created attachment 4233
Button size, show entry box in the deskbar mode.
Should work with both 4.9+ panels and earlier versions.
Cleaned up layout code to make the fixes easier.
Button size depends on the number of rows.
Text entry box is shown (if requested) in the deskbar mode.
If the text entry box is disabled the button is "small" (is laid out along columns as other button-like plugins).
Cool, thank you.