With that combination of engines, the chances of upper stage not being visible after burnout is pretty high. I launched a two staged, four engine cluster in each stage model (24 mm core and three 18 mm outboards) back in 2005 with an Astrocam as the payload and lost the model after burnout because it was so high we couldn't see it anymore, even though we heard four distinct pops of the ejection charges. The model was painted with high visibility colors and the parachute was a 20" nylon bright yellow. It was partially cloudy with blue sky. As suggested here, the fins of the booster stages were trapezoid. All four boosters were recovered close to the launch pad.
Dave, NAR # 21853 SR.,
Old Rocketeers # 724