Choose the position for access
Begin with the bag where you can comfortably reach its fastening. Open it and take out something frequently used. If you must lift the entire bag or twist your arm, alter the length slightly and try again. The visual height you prefer should be compatible with that access.
Walk a few steps and lean forward a little. A low bag may swing more, while a very high one may press against the arm. There is no correct position for every body and bag. Assess the specific model in movement rather than solely from a product picture.
The diagonal line in the outfit
A broad contrasting strap remains clearly visible. A narrow strap close to the jacket colour recedes more. Check whether it crosses a button placket, large collar or prominent chest pocket. If several details overlap, another carrying direction or quieter top can change the arrangement.
With a belted dress, two lines may meet. That need not be avoided. Check whether buckle and strap physically interfere or simply cross visually. An uncomfortable fastening is a different question from a visible contrast.
Adjust after changing layers
When a thick coat comes off, the bag may suddenly hang lower. An easily adjustable strap can be altered then. Before purchase or use, check the intended adjustment mechanism and whether it leaves a long loose end. Store that end properly according to the bag's construction.
Keep a setting that suits your usual jackets as a reference, not an unchangeable rule. Different contents change the shape too. If the bag pulls uncomfortably during a long journey, reduce the contents or choose another carrying method rather than endlessly shifting the strap position. Its colour can contribute to the outfit, but its main job remains holding the bag in a usable place.
