I have used JavaScript to make that Combo window taller. Setting in the render script or init script. U could also change the CSS deep inside so that those items are more tightly spaced.
(Since I had to specify an ID number of the field, and aware likes to generate its own unique ID numbers, it creates a problem if you open multiple tabs of the same type of BO. It’s only a problem in this situation. If you have a row operation that opens a form in a new tab, then it’s possible to open a tab to view customer A. And then tab back to your grid. And then do another row operation to view customer B. Since you overrode those row IDs so that you could find that combo box to change its height, then Aware gets confused because it has no longer has unique ID numbers for its controls. Weird, obscure, but yes it can be a problem. I have a post on this problem and will link to it later.)
So yes it is possible to do exactly what you want, with potential issues.