Hi guys,
A quick designer's note on this.
The cover/obscuring rules were written to remove as many arguments as possible where half-hidden models are concerned. The original SST rules were an attempt to remove arguments by abstracting things out - I believe the Evo rules are better, as they leave nothing for debate.
So, by letter of the rules, if you can see _any_ part of a model, you can fire at it. Removes all argument.
That said, if players wish to apply common sense and rule (even in a tournament setting) that items such as long, thin aerials do not count, you have our blessing. It is certainly the way we play in the office.