Any pros and cons between full vented and partial? i currently have partial - replacing with my siding job. Also shoud your siding go up into soffit area. or cut and butt it off where soffits meet?

Hello everyone, I am trying to put up a shade sail over my back patio. My backyard patio is in full sun almost all day. The way my house faces (Front yard East, backyard west) the only time the patio is shaded is in the morning. I planned on doing a rectangle shade sail with two mounting points on the house, and then installing two poles just past the patio for the other side mounting points. That's the easy part for me. The problem that I am having is, how to find a good solid stud or mounting point under my aluminum siding without taking a bunch of siding off? I want to put the mounting points on the underside of my second story overhang. Now there has to be some solid support right there correct? Here is a picture: [ATTACH]51725[/ATTACH] I have already moved my cable cord out of the way. From the mock-up picture it looks as though my electrical wire might be close to the sail, but it wont be. At the height that I plan on putting the two posts, there should be plenty of room between the sail and any wires. But as you can see in the picture, that is basically where I would like to anchor the sail to the house. But I don't know how to tell where there is a stud. It has to bee pretty stout so that the shade sail can be tightened down. Should that whole underside of that overhand be solid? Would there be a stud or double stud right along the joint? Thanks in advance