When in the nicu, Jace was eating 5-6 oz every 3-4 hours. Tonight he's been taking about 2.5 every 2…

When in the nicu, Jace was eating 5-6 oz every 3-4 hours. Tonight he's been taking about 2.5 every 2 hours. I know it's still the same just spread out but I'm wondering how to help him last 4 hours again. He is currently using similac spit up formula ready to feed. Delos used it too when he came home. We found with him that he stayed full longer with powder formula. Is that normal? Has anyone else noticed that?