The 10:1 ratio is in the rulebooks. Page references for Edge of the Empire given above. Neil Smith is saying that, on the FFG forums, people use a 5:1 ratio for vehicles and 10:1 for starships – inserting another scale in between the two official ones.

Personally, I use the 10:1 scaling as per the rulebook, but I do house rule criticals. Critical hits add +10 to the roll per silhouette difference upwards and -10 downwards. So a silhouette 4 starship fires on a person (silhouette 1) and gains a critical, they add +30 to the roll. The person, if lucky enough to get past armour on the starship, would reduce their roll by 30.