The DF unfortunately does not work for every lo. When my DD was younger I could not get the bottle in her mouth to do the DF. When she got a bit older and we had the 6 month growth spurt, she all of a sudden started taking a DF.
If the DF does not work for your lo, you could always try cluster feeding instead, at say 5pm, and then offer another bottle at 7 and see how things go.
I would not suggest cutting the 7pm feed down, as this could have a knock on effect and actually end up causing another night waking.
What time are you offering the DF?