Modern cars don't have flow separation at the top of the windshield where the roof begins. (OK, possibly Jeeps with the flat windshields do, but they're not cars.)
I can't answer your question about why there's a difference in water pattern, but a contributing factor could be the dramatic difference in pressure / local airspeed at the location you noticed.
Here it is in pictures, showing relative lift forces on an RX7. Note the very low pressure / high airspeed in the area you described.
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