Sorry, no. The dimensions of this dialog are fixed, also in currently latest version of UltraEdit. You could use a resource hacker tool to increase width and height of the dialog and the list elements for yourself. You can also send an enhancement request email to IDM support. The beta test period of UE v16 just started with find enhancements and therefore the moment is ideal for such an enhancement request. The dialog and the list in it could be really increased in width and height. I don't see any reason why it is so small. Even better would be customizable dialog.
Do you know that you can scroll through the list also with the keys UP and DOWN ARROW when the list has the focus? Also do you know that fast typing the first letters of the favorites title you want to edit selects the appropriate favorites item when the list has the focus. That are the Windows standard features for lists, work for example also in Windows Explorer. I nearly never search in lists by scrolling with the vertical scroll bar using the mouse and scan the lines with my eyes when I know the (file) name for I want to find. Find something known by keys in lists is always the fastest method.
You could also open %appdata%\IDMComp\UltraEdit\uedit32.ini with Notepad while no instance of UltraEdit is running or edit a copy of the INI with UltraEdit and make your changes directly on the favorites sections in the INI file. Important is that you save the INI file or replace uedit32.ini with the modified copy only when no instance of UltraEdit is running.