Like others have mentioned it's not possible to have more than 1 Cache disk per disk group. I have the same advice as the others, pleas do more than 1 diskgroup.
So in all that would mean for you (per ESXi host):
DiskGroup 1:
1 x 1.46 TB Cache
2 x 3.49 TB Data
DiskGroup 2:
1 x 1.46 TB Cache
2 x 3.49 TB Data
This way you would potentially only need 1 Cachen drive extra per host.
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