Where exactly in source axis scales are summed up when few keys bound to the same axis are pressed?

Hi, im learning UnrealEngine, now i’m at input handling.
Where exactly is the math function/method that sums values of “Scales” bound to mapping when multiple keys are registred to axis?
I have read this Input Action And Axis Mappings In UE4 - Unreal Engine. Looked in to the code and found only aggregation of delegates with axisValues.
PlayerInput.cpp contains method ProcessInputStack(…) that only aggregates deleagetes to static TArray<FAxisDelegateDetails> AxisDelegates; And then Delegates are executed at PlayerInput.cpp:1289.
But at handler in TopDownPlayerController.cpp, registred this way InputComponent->BindAxis(“MoveForward”, this, &ATopDownPlayerController::MoveForward); is invoked with sum of ScaleValues when multiple keys are pressed.
What have i missed? Where is the code that sums up values from “Scale”'s of bound keys.