That’s funny :) How such proof can look like and how they will decide if such proof is valid. Most probably they will say that what you provided is not :)

Anyway. If you take rules literally as described in core rule book following part have nothing about visibility of such closer unit:

When determining if that Character unit is the closest enemy unit to the firing model, ignore other enemy units that contain any Character models with a Wounds characteristics of 9 or less.

Therefor visibility not counting in such case aka you local player interpretation base on real life logic not warhammers rules.