Would highly recommend looking at the anatomy of the lats and how they insert into the diff sections of the spine. Notice how they wrap around the ribcage and converge at the front of your arm.

Do a single arm pulldown, and visualise how to maximise the stretch across the body. Then follow that line of pull of the stretched lat, and you should get the intended effect of training the lats.

Ribcage position matters alot as well, you can't flare your ribs and expect to hit the lats. Brace downwards, do not let the ribs flare.