What the bfing specialist told you is based on research that shows babies drink the same amount of breastmilk as they age, those that are 6 months old are still drinking on average the same amount they were at 3 months and 6 weeks. They typically never need more than 4 maybe 5 ounces per feed for an exclusively breastmilk fed baby. Waking for more feeds can be a sign of a growth spurt, and the 4 month sleep regression can start like this.
How many feeds do you typically do a day? I am exclusively pumping and I give 180ml / 6oz per feed, approx 5 feeds a day but she doesn't always finish. When my baby girl started consistently draining her 4-5oz feeds I started putting more in the bottle.
I give my baby 6oz bottles of expressed breastmilk