Tiling the handrail (upside down)?

[Ironside]

Hello,

I'm going to help a friend tile a bathroom in the basement. He also wants to tile the lintel above the door, which means some tiles need to be mounted upside down. Is it common to do that? How is it usually done if the tiles are relatively large? In this case, he has built a wooden frame to hold the tiles in place during curing, but that doesn't seem like a standard solution?

 

[Intet]

They sit like a rock without a stance.
As is well known, size doesn't matter.