Stacking double movement

[Justinian]

When stacking abilities or spells that double a movement characteristic how does one calculate the end result?

 For example I have a unit of skeletons that can move 4", Settra uses his Desert Wind ability to double that to 8" then I cast Hellish Vigour from my Vampire Lord on Terror Abyssal does this go to 8"x2 = 16" or is it 4"+ 4"+ 4" = 12" because I can't take my original movement more than once?

[Nico]

It's 16.

Just get Necropolis Knights!

[Lissë-Prime]

I read it this way:

Vampire Lord on Abyssal Terror - Hellish Vigour: "...That unit doubles its Move..." >> This one specific on Move (with capital M) i.e. "Move Characteristic". So when cast, the target unit should only double it unmodified Move.

Settra - Incantation of the Dessert Wind: "...the chosen unit can double the distance it can move..." >> This one only says 'the distant it can move' so if the distance is doubled, it should be stacked.

So in combination I'd say it can stack due to the phrase in Dessert Wind.