Iron sights being obstructed by silencers have been a common issue for many weapon designers. In previous Arma games where there was only one model, the silencer properly had measures to prevent such obstructions, as is in real life. In Arma 2, for example, the Makarov's silenced version possessed raised rear sights and a silencer with its own front sight. The silenced Berretta M9 similarly had iron sights on the silencer itself.
Referential image links: http://www.imfdb.org/images/d/d7/Arma2_M9_Silenced_custom.jpg
Unfortunately, I cannot take any screencaptures at the moment.