Different lifts emphasize different parts of the back. It's your arm path that determines what areas of your back are being targeted most. Here's how to get thickness AND width with a simple tweak to your dumbbell rows.
Dumbbell Rows for Thickness
A thicker back will give you more of that 3D look. For this, you'll want to be focusing more on your traps, rhomboids, and teres major. The good old 3-point dumbbell row does this nicely:
Plant your feet and place one hand on a bench. Then notice the path your upper arm and dumbbell travels in when doing this traditional variation.
Dumbbell Rows for Width
A wider back will help give your physique more of that "X" look that comes with wider shoulders and legs and a narrower waist. Here we're primarily talking about building your lats.
To build your lats, pulldowns and pull-ups are typically needed, meaning less allocated workout time for horizontal pulls and more for vertical pulls. But with a few tweaks to your rows, you can still hit your lats while also ticking off your prescribed dose of horizontal pulls:
Focus on the path your upper arm and dumbbell travels in when rowing.
What's the Difference?
The path of your humerus and the degree to which your elbows tuck or flare will determine what areas of the back are being hit hardest.
We're not comparing apples to oranges here, more like a Granny Smith to a Pink Lady. But these small tweaks add up to big differences over time, especially when the tweaks mean being able to get a wider back while also having better strength balance through more rowing.
Why It Works
As a general rule, where your elbow points is the direction of what's going to work. Your lats originate from your seventh thoracic to fifth lumbar vertebrae and iliac crest, where it fans upwards and inserts into the humerus.
If the line your elbow is pulling in points towards your iliac crest (towards your hip) then the row will somewhat bias your lower lats. You might have noticed this more in the second rowing variation.
On the other hand, if your elbow points higher it's more flared and your focus is on driving it BEHIND your back. More of the emphasis will be placed on your mid-back. This is how most traditional rows are performed and what you might have noticed most in the first 3-point row variation.
The degree to which you flare or tuck your elbows purposefully, as well as how you angle your body, makes a difference as well.
For more thickness, drive your elbows behind. For more width, pull more towards your pockets. In either circumstance you'll be adding to your weekly prescribed dose of rowing volume.