How the deal works seems a little unclear. Below is what I posted over on TMP - I think I have it right. ;)
My understanding and the way I did my order: A "pack" is a SKU – basically the RAFxxx number. For non-1889 lines that usually means 3 Cav with riders or 6 foot figures.
Space 1889 figure SKUs are per figure. A "pack" then is 6 foot figures of the same SKU or 3 Gashant (remember riders are separate).
I do NOT think it reasonable to expect RAFM to honour the 20 figure SKUs – canal martians, high martians and soldiers of the queen as a "pack".
Ok now we know what a pack is we can move forward. You go to the special sale page and select the package of 4,8,12, or 16 packs that you want. Pay for it through the usual methods. Then you open up your email and create an email stating the name and shipping address you just used in your order. Then you list how many packs of each SKU you want. e.g. RAF1817 x 1 will get you 6 Canal Martian Infantry figures and RAF1817 x 2 will get you 12 Imitation Legionary figures. Send that email to onlineorders at RAFM.com and you are done
I hope that helps. :)