If you are seated and the humerus is “tracking” in the horizontal plane, or transverse plane, this is not targeting the low traps, but in essence the rhomboids and mid traps.
Also, lying prone doing horizontal reverse flyes does not target the low traps, but the posterior deltoid.
Seated rowing with the humerus tracking in the horizontal plane. This means using a straight bar, not a triangle bar. Also try doing a pull-down with no elbow or shoulder movement, only shoulder girdle depression. It’s the best way I know to isolate the lower trap contribution to scapular depression. Also, doing horizontal reverse flyes with dumbbells while lying prone on a bench. Keep the humerus at ~45 degrees of shoulder abduction.
Yes better yet is standing with palms up and pulling from above with elbows bent at 90 degrees down to chest. Squeezing the lower traps at end range.
The best is prone with your palms down, arm abducted slightly(~30 degrees) and raising from floor to bench level
Low traps are not worked enough and properly!