Visual signals are a must for good spotting. If you must relay signals to the pilot, make sure your relay person also uses visual signals. You don't want your corrections to be misunderstood because someone else didn't use hand signals. You don't need to give corrections on the base leg before jumprun or even on jumprun if you're 5 miles out. Wait until you're less than two minutes and preferably less than one minute out from the spot.
Most pilots throttle back on jumprun when they get close to the spot.
They may or may not throttle back to a full cut, but they usually slow the aircraft's airspeed from full flight. You should realize that this means you're close enough to give corrections. Also watch your ground speed decrease. Before any corrections can be given you have to know where you are going. You must watch the aircraft's groundtrack to determine where you are going.