How do upgrades work?

[KrogothFTW]

More specifically, is there any bonus, besides the factory's own extra build power, applied to upgrading to a higher level factory? Is the original cost of the t1 (or t2) factory discounted in the price of the new one, or do I pay as much mass and energy upgrading as I would building a brand new one? I've realized that one must upgrade to an t2 HQ before building separate t2 factories, but we could still compare the cost of building a second HQ to the cost of upgrading a second HQ, or upgrading to a support factory vs. building it new outright.

[KrogothFTW]

What does "DifferentialUpgradeCostCalculation = true" do (from unit blueprint)

[ZLO_RD]

When t2 engy makes t2 slave fac from scratch, it costs "x"
When you upgraide t1 fac to t2 slave fac it costs "x - fac cost"

[KrogothFTW]

When t2 engy makes t2 slave fac from scratch, it costs "x"
When you upgraide t1 fac to t2 slave fac it costs "x - fac cost"

That's what I thought. Doesn't look like shield gens get that treatment.