1) Launch probes from an offscan spot, get them hidden by dragging them 20+ AU above or below the plane of the system and running a scan, then warp to a safespot in scan range of the target
2) Locate the target with your directional scanner. You'll need to get the range to the nearest AU* and narrow the angle down to at least 15 degrees; 5 is preferable
3) Open the solar system map, activate the tactical overlay, and hit F11 to bring up the navigation panel on the right of your screen.
4) Move the map camera such that you are looking 'down' on the plane of the system, then rotate the view such that the orientation of the system in the main map window matches that in the bottom window of the navigation panel.
5) Note the green cone** in the lowest window of the navigation panel. This indicates the area of the system covered by your narrowed-down d-scan. By comparing it to the main map and using the distance indicators provided by the tactical overlay, you can tell where the target is to within one cubic AU or so.
6) Run your first scan with probes at 4 AU, at the appropriate location. I use a 5-probe formation like that shown by EKR in the OP, but with the 'outer' probes at 4 AU and the 'inner' at 1. With max skills, this should net you a 100% hit on anything the size of a shield-tanked cruiser or larger. If your first scan is slightly off, move your probes to 'centre' of the first hit and re-scan without adjusting your probes' formation or radii; the second should certainly nail them.
* Note that 1 AU = 150,000,000 km (and so 7 AU = 1050,000,000 km and 14 AU = 2100,000,000 km, etc. etc.).
**Sometimes this cone doesn't show up when you first hit F11. If so, adjust the d-scan angle up a notch, then back down to its original value; this should cause the cone to appear.