GTK 3.20+ Custom Start Menu Button for Themes - Sizing is Off

[OwN-3m-All <own3mall gmail com>]

Hi All,

Before GTK 3.20 was introduced in Ubuntu 16.10 with MATE, the custom theme I maintain used a non-standard start menu button image which worked fine.  It was placed in the /usr/share/icons/THEMENAME folder under the 22x22, 24x24, and 48x48 /places subdirectory.  The size of the image in each location was 107 pixels by 30 pixels.  

With older versions of GTK and MATE, the icon would render at its actual size despite being in one of the folders listed above specifying it *SHOULD* be that size.  Now, it is clipped and behaves strangely.  Is there any way I can render a non-standard start button image without having to make it a small square like all the other theme's start menus?  Surely there is a way to adjust the size of the start menu?  If there is, I haven't found any way through the gtk-widgets.css or through any other file.

I appreciate any help with this.  I'd really like to use a wider custom start button that doesn't get clipped like I could in the past.