Multiple tablix within same report

I have an RDL using one dataset, but will 3 tables/tablix (based on status filters).  Two of the tables are side-by-side. The third is below the top right table, which is usually very short. My problem is that the third table moves down based on the left side table, which can get long.

How can I anchor the left bottom table to the length of the top right table, irregardless of the length of the top left table? I am using VS 2013 to create SSRS reports.

This gives you an idea of the proportions, though they change.

XXXXXXXXXXXXXX              XXXXXXXXXXXXXX
XXXXXXXXXXXXXX              XXXXXXXXXXXXXX
XXXXXXXXXXXXXX              XXXXXXXXXXXXXX
XXXXXXXXXXXXXX
XXXXXXXXXXXXXX
XXXXXXXXXXXXXX
XXXXXXXXXXXXXX
XXXXXXXXXXXXXX

                                         XXXXXXXXXXXXXX
                                         XXXXXXXXXXXXXX
                                         XXXXXXXXXXXXXX
                                         XXXXXXXXXXXXXX
                                         XXXXXXXXXXXXXX
                                         XXXXXXXXXXXXXX
                                         XXXXXXXXXXXXXX
                                         XXXXXXXXXXXXXX
                                         XXXXXXXXXXXXXX
                                         XXXXXXXXXXXXXX