"If the target model is partically obscured by another model line of sight is blocked and another target must be chosen."
Is this correct?
I whoudl guess it should be: "...another FRIENDLY model"...
It does change Overwatch as the partially intervening enemy can not be chosen as a target instead (only the activating enemy model partially behind).
In normal ranged attacks it seems strange (firing with sight partially blocked by terrain possible but not partially blocked by enemy models). Allied models are a better cover than terrain?
It totally makes sense you can not fire past friends risking to hit them (without some m-power or special gear/zone stuff).