Ah, that does make sense. I do think the chances of something popping up in the six months since you've been discharged are extremely low (like go-play-the-lottery low) and I will say I also have an indent of a similar size on my breast that is also next to a scar and that I ask about annually and am told it's totally normal. But I understand your fear; I find myself analyzing every stretch mark to see if it's a concerning indent or just a normal body mark.
I will say based on what I've been told from my own doctors, that concerning indents are usually really obvious (often sizable) and you know they're out of place. I would believe that it is just scar tissue as well. But I also know how hard it is to tow the line between health anxiety and being proactive.