Also, if you’re not already, consider using straps for all of your pull-downs & rowing.
Some guys only use straps for their heaviest set(s), but I use them for ALL working sets.
It sounds like you’re concerned more with aesthetics rather than functional strength.
Straps allow you to focus more on pulling with the back instead of the bi’s, and IMO will give you the best results for what you’re after.
And, when fastening in, try to get your palms “over” the bar as much as you can.
This will also help minimize bicep involvement.