I don't understand why 3d has higher energy than 4s orbital...?

I have read that atoms heavier than copper exhibits what normally should be the case , ie, electron farther from nucleus will have more energy, but in atoms lighter than copper a 3d orbital has higher energy than an 4s orbital../so why in atoms heavier than copper we have 3d orbitals lower in energy again than 4s orbitals ...why follow different rules for atoms heavier than copper & for atoms lighter than copper...thanks in advance.plsss make me understand this