Hi,
Everybody has a different Joomla Template, therefore the necessary CSS rules might be slightly different from person-to-person. Because those are custom changes. If you copy-paste the same exact CSS lines that provided in here, things might not work for you as expected. Furthermore, you are using a different Browse page layout (yours is flexv3)
Beside, that client has knowledge on CSS, he have already taken care the box equalization. He just asked a TIP to align the bottom section to the bottom level.
You should use "Firebug" for CSS touches. It must be your number#1 development plugin to use while doing that kind of changes.
Use a fix height value for the
.FlexibleHover2 {...}
First, retrieve your changes back to stock and try these instead:
.FlexibleHover2 { height:360px;overflow: hidden;}
.flexv2 #GridView .FlexibleBrowseThumbProductLower { height:100%;}
this should equalize the height of the boxes. IF you are looking for a more professional method, then you can use jQuery .equalizer();
css-tricks.github.io/Equalizer/
Since, it is a 100% custom changes, i can't provide you any further guidance on this. You may consider purchasing premium support through:
www.flexiblewebdesign.com/premium-support
Regards.
Support