You cannot, but I can, in theory they all have the same probability. BUT, they have a "range", if the mission is set to 13,13, then you can accept the mission if you are withing X hexes of that location. I can change that X to any value, but in most cases I keep it down to 1 or 2. By default, Scan is set to 5, I changed it to 1 or 0, so it should appear less.
And yes, you're free to mirror them on sfcx.org, I was going to send you a link, but haven't gotten around to it yet. There's plenty of bandwidth on my site for that size of download (I have 30GB actually), but I still can't put my DW mod on there, it'd wipe out my limit inside a week.