The Resurs-P1 satellite had a mass of 6,000 kg and was at an altitude of 355 km when it broke up. ISS’s orbit is about 415-420 km in altitude, I believe.

Break-up events can sometimes cause the apogee of debris to increase, but that usually coincides with a corresponding decrease in perigee. Thus if the apogee gets too high, the perigee is dropped into the atmosphere, and that piece of debris doesn’t last too long. Still, a potential orbit of 255 – 455 km would be possible, so it was probably wise to sit tight for an orbit or two to let the worst of the debris get tracked.

I’m not an expert in the field, but it seems reasonable.