Powermax and Storage Group restrictions, limitations... seeking some discussion

New to Powermax but familiar with Arrays.  I'm stumbling with Storage Groups (SGs) and encountering  restrictions - thus seeking other opinions/direction or best practices. EMC professional services got us started with the below standard and we are continuing . Here is an example of a restriction and ask for your opinion…

SG_ParentA-(SPR: None) .. SG_ChildA-(SPR: 01) ..... disk_1, disk_2, disk_3          (masked to … HOST_A)

SG_ParentB-(SPR: None) .. SG_ChildB-(SPR: 01) ..... disk_1, disk_2                        (masked to … HOST_B)

Suddenly we have a requirement to have disk_3 visible to both Host_A and Host_B. We cannot add the device to both SG’s without error: device cannot belong to more than 1 SG in use by FAST….

I’ve even tested with Parent-child SG’s but just Storage Groups….

SG_A-(SPR: 01) ..... disk_1, disk_2, disk_3     (masked to … HOST_A)

SG_B-(SPR: 01) ..... disk_1, disk_2                   (masked to … HOST_B)

Fails again when trying to add disk_3 to SG_B (and coexist in SG_A)….

Any suggestions… is this normal…. What have we gotten ourselves into? Please understand that its up to the hosts not to corrupt the volumes, etc… but this is a normal practice in clustering software or in SOLARIS….