Considering the green pool and overhead features, the first thing drawn of that was likely the bottom line of the pool. It was not possible to draw the nymphs' legs without that line. I imagine the overhead thing was then drawn with "the same" slant as the pool, using the nymphs' heads as guidance for where the bulbous protrusions should be.
The reason for the slant then appears pretty straightforward: the base line for the pool is uneven, moving up and down, throwing off all sense of orientation. Everything after that had to cope with the slant. It's like one of those medical diagrams where a slight difference in leg length can lead to shoulder problems.
The reason for the slant then appears pretty straightforward: the base line for the pool is uneven, moving up and down, throwing off all sense of orientation. Everything after that had to cope with the slant. It's like one of those medical diagrams where a slight difference in leg length can lead to shoulder problems.