Shower tray with 4 upstands ???

[nyck]

Looking to replace a old leaky shower .
I seen a new Mira Flight shower tray on Ebay ,quite cheap and local but it has 4 upstands .
I thought the whole point of the upstand was you tile over the upstand for a better seal .
I can see how it works for 2 upstands tile 2 sides + Door and side panel , 3 upstands tile 3 sides + Door , but with 4 upstands how does that work ....confused

 

[cdbe]

Presumably you fit the door inside the upstand. Mines a 3 upstand (also cheap from eBay) but could have worked with a four.

 

[avonmouth]

three panels and a door.