This configuration generally not allowed. BC810 is used for module redundancy (here for SM811), so it allows you to configure the redundant SM at 1(7) position by default from Control Builder and the redundant position (i.e. 1st at primary and 7th as redundant) is non-modifiable. So, it is always advised to used BC810 along with PM865 redundant configuration. However, with the use of CEX cableds you can make SM811s redundant to each other. But you can't achieve the redundant position of SM811 at 7th. Instead it will be 1(2). And there is a hectic procedure to bring the hardware configuration to 1(7).
As per the product safety manual HI controller must always be installed with BC810s. The certified system architecture for HI controller is with BC810 - however, I have not been able to find an evidence of this.