masonry issues at different screen sizes

Hi,
Just wondering if you can help me resolve an issue with the homepage we are developing.
It can be viewed here http://www.proactiveproperty.com.au/home-3/
We are trying to use a masonry gallery, stretched full width, using the ‘Perfect Automatic Masonry’ option. This views as desired on my desktop and responds nicely on my smart phone BUT we are finding an issue with the screen size native to an iPad. The last graphic at the bottom right (with the text ‘joint ventures’ on it) drops to the row below, and sits by itself, rather than staying on the far right hand side as intended.
If you view this page and slowly resize the browser width by dragging the browser window in from the right, slowly to the left, you will see that joint ventures graphic jump to the row below, and then back up and then back down again, as you make the window width smaller and smaller, before it moves to a smart phone sized window.
Is there a way to prevent this from happening? We’d like the masonry to effectively maintain its form as 3 rows until it reaches the smartphone size, rather than toggling between 3 and 4….
Hope this makes sense?!
Thanking you in anticipation.
A