RCD's in series and how to test

Im currently working on a site where im testing the supplies to the site cabins. Each cabin has its own 6 way single phase DB with a double pole RCD as a main switch. The DB's are then fed via commando plug and socket arrangement from a 32a RCBO within a TP&N DB. When the cabins were originally 1st fixed the dead tests were performed and recorded ( r1-r1, r2-r2, rn-rn, R1 + R2 and IR ). Now i am in the process of energising the cabins and performing my live tests and as you can see have two RCD's connected in series.

In each cabin i have turned the main RCD switch off and in turn performed my RCD test on the supply side to prove the tripping times of the 32a RCBO back in the main DB. My question is will the readings ive obtained here be suitable to record as my RCD tripping times when i fill in the test results for my final circuits within the cabins? All the readings are within permitted values, only when i turn on the main RCD and try to perform the same test on the final circuits the RCBO in the main DB trips at x1 and the main RCD in the cabin DB trips at x5. Meaning that i havnt been able to prove that the main RCD in each cabin trips out at within the required time for x1.

Im not sure why there are two RCD's connected in series like this as i havnt done the design. I would have thought the RCBO in the main DB would have been more than adequate