I wonder how to add more weight to a dumbbell.  

Adding more plates of fewer weight or fewer plates of higher weight?

With bigger plates the diameter grows and so will the minimum distance the dumbbells will have to your body.  

With more plates on the handle however the center of the handle itself will be farther away from the body - eg. when placing the plates on the shoulders while doing front squats - and it might be harder to balance the dumbbell as the weight is farther away from the center as well.

I already bought rubberized cast iron plates, not those concrete filled plastic plates, as reviews on amazon complained about the overall size of the latter.

Do I have to worry about this at all when buying weights for my dumbbells?

As per request I drew a diagram:

![dumbbell distance](https://i.stack.imgur.com/n1NIs.png)

Imagine this to be the resting position of the dumbbell on the shoulder when doing a front squat, viewed from the front. The brown line below the dumbbell resembles the shoulder, the brown block is the hand. The plates are on the shoulder, the handle itself goes down behind the back.  

With only one plate the hand is closer to the shoulder (red line), this also affects the angle of the elbow. However the hand is farther away from the head (blue line).  

With the three smaller plates the hand is higher up, but the dumbbell can be held closer to the head.