Mark1515,   When mixing memory modules with different capacities, populate the sockets with memory modules with highest capacityfirst. For example, if you want to mix 16GB and 32GB memory modules, populate 32GB memory modules in the sockets withwhite release tabs and 16GB memory modules in the sockets with black release tabs.   Let me know if this helps.    
What would be the optimal memory configuration for an R730xd with dual processors and 8 32GB plus 8 16GB ram modules? We currently have 8 32GB and 4 16GB modules installed and working.
R730xd OptimumRAM Config for 8-32GB and 8-16GB (Dual Processor)