Installing two memory modules of different sizes (PowerEdge T20)

Hello! I am planning on purchasing a couple of PowerEdge T20 servers, and I have a question about combining two memory modules of different sizes. To begin with, the online configurator won't let me uncheck the default system memory module, which is "4GB (1x4G) 1600Mhz Single Rank x4 Data Width UDIMM LowVolt". I'm wondering if I could purchase an 8GB memory customer kit and install both memory modules so that the total system memory would be 12GB and it would work properly. The Dell website doesn't reveal too many technical details about available memory modules for T20 to purchase, so this is all I know about these two modules:

• 4GB (1x4G) 1600Mhz Single Rank x4 Data Width UDIMM LowVolt (default)
• 8GB Memory, 1600Mhz, Dual Ranked UDIMM (Customer Kit)

This is what the User's Guide says:

A maximum of two UDIMMs can be populated in a channel. Populate all sockets with white release tabs first, and then black. Populate the sockets by highest rank count in the following order — first in sockets with white release levers, and then black. Memory modules of different sizes can be mixed only if other memory population rules are followed. For example, 2 GB and 4 GB memory modules can be mixed.

So, will it work if I for example install the 4GB module into socket 1 and the 8GB module into socket 2?

Thank you in advance!