A couple of things - if it works go with it! Your LO will change everything when you think you've got it down!
4, 6, and 8 cluster feed is pretty common. You could try a bottle of EBM at the 6pm feed - from what I understand milk supply decreases as the day goes on so I would sometimes pump at 6 and 8 but give LO a bottle at 7pm and that held her over pretty well.
I also have seen some routines where LO goes to bed, then wakes for the 8pm feed, then goes straight back to bed. I used that one for a long time and now at 6 months she grew out of it.
HTH!