I always think F=Ma. The force is depended on the mass since the acceleration is usually similar due to friction and compressibility. Mass is the size of the aircraft. So if the mass is equal to or greater than the one your in, it can have an influence. You might feel a sudden jolt from a smaller aircraft. My primary concern is the actual size of the wake itself. A large aircraft capable of a large wake and a light quartering tailwind are usually conducive to a threat.
The real threat to any aircraft is when you get sort of stuck in the vortex. When you fly through it, it's just like violent turbulence. But when it follows your flight path and your control-ability is affected, it may last a long time causing a loss of control.
Rare, but a not so fun situation.