Mega Menu with Images – Vertical Alignment Problem

I have a website that’s been in development for a while. (I’ve included a link to its temporary location.)

There’s an issue with the mega menu (that appears when you hover over Treatments).
There are five submenus, each of identical column widths.
When the browser viewport width is 1304px or above, all the images appear at full-size (200px wide) and there is perfect vertical alignment of all menu headers and text.
However, when the viewport width is less than 1304px, the images in the two outer columns (ie. far-left and far-right) remain at 200px wide, but the images in the three inner columns become progressively reduced as the viewport becomes narrower. Once the viewport becomes 1232px wide or less, the two outer images then start reducing in size too, but never matching the three inner ones.
The problem this introduces, is the vertical misalignment of the menu contents, as the two outer ones no longer match the inner ones and the menu content in those appears to have stepped down a little in relation to the three inner menus.
(Note: All five column containers’ pixel widths remain perfectly matched no matter the viewport width.)

My client’s viewing conditions are on browser windows less than than the magic 1304px, so they are always seeing the vertical misalignment – and want it fixed.

I’d be grateful if you can tell me what file setting to adjust, or CSS change to make so I can keep my client happy and finally get the site launched.

Thanks very much for your time and any suggestions you can make.