Have you tried resettling at the 4m feed or do you just feed first?
If you don't think the DF is making any difference then you could always stop for a few days and see what happens. However, 5 months is still young to be going from a DF to morning, it's very normal to still be having a DF and a NF. Most babies don't drop the night feeds until they are established on solids really, some will sleep through by themselves before that but more don't.
Laura