Those names are based mostly on shape of mildfield;
V formations hae mildfield like:
AML------AMR
---MC--MC--
-----DMC
Narrow formations are ones which doesn't have wingers in mildfield: DML, DMR, ML, MR, AML or AMR
Narrow diamond has this shape of mildfield:
--AMC--
MC--MC
--DMC
Wide diamond has this shape of mildfield
---AMC--
ML----MR
---DMC--