«ضَرْب» and «عِلْم» may be equal in length, yet their consonantal material differs considerably. Equal letter count alone therefore does not establish jinās. Likewise, sharing a morphological pattern, as with «ضَرْب» and «قَتْل», is not by itself sufficient.
The figure concerns an audible or orthographic relationship between expressions, not simply the same grammatical position or morphological paradigm. A common pattern may help explain resemblance, but the relationship between the actual letters must still be examined.
This prevents confusion between the grammatical concept of pattern or meter and the rhetorical figure of jinās.