Flower nems are like any other. They move when they feel like it. There are no guarantees in anything.
One thing you might try for feeding would be a small piece of silverside soaked in garlic.
Additionally, there are people who *NEVER* feed their aneomnes and they pick up plenty of food in the water column. Granted, people do some weird stuff, but I'm curious as to how the flower appears to you. Does it look distressed? Shrinking? anything else? If not, then feeding isn't a huge issue for it.
The BTA on the other hand will move when unhappy. Just let it figure out where it wants to be, and get food to it whenever you can.