@andythom188 , had a thought about your van shades m8, might be OTT, but will suggest anyway...
Before fitting the rears, try the sliders.. The reason I say this is in case they have movement vertically, and you land up fitting the rears first at a higher height than the sliders? Masking tape on carpet and a pen mark showing level of top/bottom of the blind at trial fit?
Might be a bit OTT or OCD?