I really believe every dog is different. Some dogs self-regulate pretty well, while others will eat until they pass out. I used to just free fed and leave food out all day, and Jackson some days would barely eat, other days he'd finish the bowl. I used to put 1 cup into his bowl and he usually just only ended up eating 1/2 cup so I figure that's all he really needs.
We've had an ant problem here where we live so I cannot leave food out all day anymore so I've been feeding my 16lb Jackson 1/4 cup of dry food (Acana grainfree) mixed with wet food in the mornings (usually around 9am) and then 1/4 cup of dry food again in the evening also mixed with wet food. So all day long he gets 1/2 cup total (plus whatever wet food) and it seems to fill him up really well and he's at perfect weight and really really active.
Stop looking at "cups" of feeding and start looking at calories. Consider any treats also. There are a few different calories calculators for dogs online, they vary some but the good part is, each gives a range for a variety of activity levels. Acana Grasslands (what we feed) is around 430 kcal/cup. If I was feeding a food like Pedigree, he would need a lot more (probably 1 1/2 cups a day or something) but Acana is pretty calorie dense. He also gets quite a few treats (Wellness soft treats & Zuke's Mini Natural's for training, and 2 of these:
http://www.avenuek9.com/wp-content/uploads/milkbone.jpg a day, which are around 15 calories a piece, I think).