[SFConservative]

I believe it is supposed to float so it can accommodate a significant amount of thermal expansion. The diagram above suggests how its shape registers it to the RCC panel on the left while the panel on the right can slide as the overall assembly expands and contracts while maintaining a reasonable seal. The dimensions are chosen to ensure that the T-seal stays captured under worst-case thermal expansion.

[SFConservative]

OOPS - as I look at it again, it does suggest that it is bonded somehow to the RCC panel on the left and floats against the one on the right. More searching needed.