DS1 was 8 months when he started fdc and he did have formula in a cup during the day. But he seemed to be ok with it, it kind of sounds like your DS doesn't like it very much

DS2 was 11 months when he started at fdc and in the beginning i was giving him some EBM but was unable to keep up with having enough with storage. After asking a few questions myself i just include a little more dairy in the days he's in care. Cheese, yoghurt etc...

I too feed about 6:30am and then again at 4:30pm when i pick him up, we do this two days a week.

Also with the possibility of him wanting to drop a feed mentioned, it just made me think that formula is said to be more filling than bm so maybe he's not needing it as often as he would if it was a bf because it's filling him up longer. Just an idea

HTH