Rear of Y always dirty - why?

[Eto Demerzel]

Does the MYP's spoiler "help", even if a little. Do MYP's backside stay cleaner than MYLR? As someone mentioned, I wonder if a diffuser will help, too. Thanks.

spoiler will make it worse and probably makes aerodynamics a tad better by increasing the low pressure zone.. It's aerodynamics. Suv's have this as does any vehicle with a kamm tail or large, low pressure zone behind it.