The Mazdaspeed dampers are the same part numbers, so I'd assume they are the same length. You could check the parts department and if the stock ones share the same p/n, then it's 100% confirmed.
How can Mazdaspeed (high performance) damper p/n been the same as OEM?
I am only guessing Mazdaspeed dampers are designed to work with shorter springs like Bilstein Sport.