Cutting the spike all the way down is fine. It's really just a matter of your method. You'll figure out what works best for your plants and your growing.
A Dtps. is short for Doritaenopsis. it's an intergeneric hybrid between a Phalaenopsis and a Doritis. i have one that likes to be cut all the way back when finished blooming and another that is much happier reblooming from the same old spike again and again.