jkhawaii, Watch out for volcanoes. My advice to you. (You're welcome.)
Your short trips are probably what is elevating the iron levels a bit. When the engine bearing surfaces are relatively cool, the ZDDP layer doesn't become effective yet. And the normal diesel soot in the oil doesn't help the softer cold tribofilms work effectively enough (compared to low soot & particles in gasolone engines). Result: Iron per mile goes up.
You are using a quality dexos2-rated oil, so no problem there. Any dexos2 oil should get you similar results.