And here comes the second question; what should be the minimum distance to get closer to another aircraft? Same problem we had; what I ve been told is that it should be 50 m. minimum
And much depends on what you are and what they are. A PA-31 behind a B747 is >50m. You'd get airborne if they went 40% break away. I was very nervous when I was in front of a B747 and I felt his shadow cover me like a shark over a scuba diver. I doubt he could even see me, so I reminded him I was first and still there. I once heard (rumour) of some guys in a DC-9 type a/c, who were getting close to their hold-over time during a lengthy taxi in USA, and it started to snow again, that "maybe we should get it close to the B747 jet blast and clean the wings a bit?" An A319 or EMB135 behind an A380 might be shaken not stirred if too close.
It's not an exact science, more common sense.