For the best accent affect, the direction of the lighting should be same as the viewing direction, therefore the accent lighting should be ideally located slightly in front of the display counter.
Luminaires should be placed so that they do not have to be tilted more than 20o. If they are placed further away, this angle will be greater, which will increase the risk of direct glare for the staff and customers casting their own shadow on the display counter.
Accent lighting illuminating the back shelf/wall can be tilted more than 20o, since their risk of causing glare is minimal. However for adequate light mixing, the offset from the shelves/walls should not be smaller than 70 cm and ideally be 90 cm.