Jamming support for an attack comes in roughly two geometries, and the difference lies in where the jammer is relative to the threat range.
Stand-off jamming
A specialised platform jams from a long distance, safely outside the range of the threat. Advantage: the valuable jamming aircraft runs little risk. Disadvantage: because of the long distance the jamming signal has a long way to travel, so a lot of power is needed and the effect is weaker (see burn-through, Burn-through and the J/S ratio). Historical examples are the EA-6B Prowler and the EC-130H Compass Call (communications jamming).
Stand-in / escort jamming
The jammer flies with the strike package, close to the threat — sometimes right in the middle of it. Advantage: because of the short distance the jamming signal is much stronger and more effective. Disadvantage: the platform shares the package's risk. The modern example is the EA-18G Growler; on the unmanned side there is growing use of stand-in jammers on drones and of the MALD-J (Decoys and saturation), which remove the risk to a crewed aircraft.
The choice between stand-off and stand-in is a trade-off between effectiveness and risk, and it is determined by the physics of the jamming signal: the closer the jammer, the more jamming power falls on the radar. That is exactly what the burn-through calculator below works out.