Note that the module does not follow the VITA57 height constraint. It has an additional daughter card that mates to the FMC module to allow it to accommodate the six ADC channels. For example, on the AMC FPGA FMC Carriers, it requires a full-height AMC panel to accommodate all the I/Os.
The Carrier must have a monolithic panel (the FMC255 does not come with an FMC panel) to cover the FMC255 I/O envelope.