Mandevilla Alice DuPont is Mandevilla x amoena and NOT M. laxa ... they are two different species. For my M. x amoena I overwinter it in my greenhouse and it gets cut back to within 3 inches of the soil line and watered very sparingly until I start to see new growth around March.
I'm growing M. laxa at the moment, started from seed .. it's extremely 'fragile' the first 2 years from seed so I don't cut it back and keep it in the highest point in the greenhouse for warmth over the winter.