I currently have the role of the lead reviewer you describe and I often worry I'm focusing too much on minor details. Fortunately my coworkers are comfortable pushing back. I think if you're able to have an objective discussion and agree on your goals, and whether a suggested change meets them better than the existing code, you'll be able to get work done together without one of you feeling like you're being a problem. The reviewer also has to be prepared to let go of a suggestion if the change won't have an actual impact.