"I recently aquired ObjectDesktop Plus, and after some browsing of the menu loaded in the 'default.ini' theme"
Do you mean ObjectDock Plus? I don't know what you mean by browsing the menu and loading in the default .ini theme. Does this mean that you clicked on the "Configure ObjectDock" icon, and chose a background in the Appearance section?
In any case, try clicking on a "Configure ObjectDock" icon, and click on either "Size & Appearance" if it's a tabbed dock, then click the "Adjust tab colors and styles" button, and from there adjust the icon size, or click on "Appearance" if it's a zoomer dock (as it is in your shot), and adjust the icon size from there.