horizontal size of GtkToolButton

[Allin Cottrell <cottrell wfu edu>]

Various windows in my app have toolbars containing GtkToolButtons. I'm 
trying to achieve the same basic look in gtk2 and gtk3.
The buttons are icon-only and the icon size is 16x16. In gtk2 
(2.24.25) the buttons come out at 28x28 pixels (as determined via 
gtk_widget_get_allocation) while in gtk3 (3.14.7) they're 34x29. The 
code generating the toolbar is in common, and the theme is current 
Adwaita in both cases.
I find that the gtk3 behavior, a button width of 34, makes the buttons 
too widely spaced horizontally and doesn't look as good as gtk2. I'm 
aware that gtk_widget_set_size_request cannot be used to make a widget 
smaller than its "natural" size in gtk3. Does anyone know of any other 
way of shrinking the horizontal size of GtkToolButton? (I've tried 
manipulating all the seemingly relevant properties I could find, to no 
avail.)
I've put an illustration of what I'm talking about at
http://users.wfu.edu/cottrell/tmp/buttons.html
Thanks for any help!

--
Allin Cottrell
Department of Economics
Wake Forest University, NC