Here is some pics to show how they made the rear end tighter and how the "bulge" became pronounced:
Beginning of the season:
A few races ago:
Most recently:
Also a pic of the rear end with the gearbox and suspension exposed; notice how high the suspension is mounted, and hypothetically where the "bulge" would appear under very tight bodywork.
So you can tell that at the beginning of the season, there was one big hump that actually bulged near the exhaust. Now, the bulge is much smaller, but a bit more pronounced because of the two "bumps" sticking out. They are more pronounced due to tighter bodywork. There is no longer a bulge near the exhausts, the bodywork has become much tighter in that area. Use the horizontal suspension members as reference points in terms of how much fatter and bulkier the bodywork was at the beginning of the season compared to now.