>>1494762I didn't even think of them because that other guy already got it right. Those solid lines in the plan are a change in surface height visible from the top and they're certainly not showing it going down. Here they're a 10 mm rise between the arrows I've added and the top surface extends through the cyan circled region. This adds a lot of strength to the vertical elements. With them about 50% of the height has support, without them about 65% is unsupported.
The lines in red are the walls of the central well which again can only extend where there is material. If the central section was not raised the central well would have to stop at the dashed yellow line I've added to match the flange height but the well walls extend to the top of the 33 line. There's no reason for that 33 dimension except that the central region is higher than the 23 mm high flanges at each side.
