The problem is US law in the early 20th century limited the house to 435 seats, which negated much of the population advantage in representation. It's no longer closely proportional as it was intended, because even sparsely populated states like Wyoming still need a rep whereas large states like CA and NY don't get as many representatives per person. I think the stat is something like 30% of the population gets 70% of the vote, and this carries over to the electoral college.