Hi Neil,
I have attached a photograph to assist. At the top of the frame we have 1 x 20mm seal. then on both hinge sides (double door set FD30) we have 1 x 10mm seal.
Hinge sides of both leaf we have 1 x 10mm and they will meet with the frame seals if they expand.
On one Leaf where the doors meet when it closes it has one x 10 mm seal.
I take this is incorrectly fitted, or replacement doors with 10mm seals
20MM X 10MM.pdf