Lightroom: Profiles Thumbnails too large - Allow me to set a preferred size

I'm assuming your are running LR/Classic and are referring to the profile browser in the Develop module (accessed through the Basic panel).   In case you didn't already know, there are 3 views of the browser you can use.  "Large" uses the entire width of the riight panel for previews of your photo using each profile.    "Grid" shows much smaller previews side by side with the number across depending on the current width of the right panel group.  And, "List" shows no previews but as with the others if you hover your mouse over any profile the image in the central part of the screen snaps to that profile (it doesn't assign the profile unless you actually click on the profile.

Select the desired view using the drop down at the right end of the 2nd bar under the "Profile Browser" panel headers (the line that says All Color B & W).