@drwprz, take a look at the list below. As you correctly noted, it’s not surprising that the best schools have the smallest class sizes, whether they are undergraduate focused universities or LAC’s - yes there are outliers that have larger graduate populations, but it’s far from the majority.
1 California Institute of Technology 34-35
2 Harvey Mudd College 33-35
3 Massachusetts Institute of Technology 33-35
4 Columbia University 32-35
5 Harvard University 32-35
6 Princeton University 32-35
7 Rice University 32-35
8 University of Chicago 32-35
9 Vanderbilt University 32-35
10 Johns Hopkins University 32-34
11 University of Notre Dame 32-34
12 Washington University in St. Louis 32-34
13 Stanford University 31-35
14 Yale University 31-35
15 Amherst College 31-34
16 Brown University 31-34
17 Carnegie Mellon University 31-34
18 Duke University 31-34
19 Haverford College 31-34
20 Northeastern University 31-34
21 Northwestern University 31-34
22 University of Pennsylvania 31-34
23 Williams College 31-34
24 Bowdoin College 31-34
25 Hamilton College 31-33
26 Cooper Union 30-34
27 Cornell University 30-34
28 Dartmouth College 30-34
29 Georgetown University 30-34
30 Pomona College 30-34
31 Boston College 30-33
32 Case Western Reserve University 30-33
33 Colgate University 30-33
34 Georgia Institute of Technology 30-33
35 Grinnell College 30-33
36 Tufts University 30-33
37 University of Southern California 30-33
38 Vassar College 30-33
39 Washington and Lee University 30-33
40 Swarthmore College 29-34
41 University of California—Berkeley 29-34
42 Carleton College 29-33
43 Claremont McKenna College 29-33
44 Emory University 29-33
45 Reed College 29-33
46 University of Michigan—Ann Arbor 29-33
47 University of Virginia 29-33
48 Wellesley College 29-33
49 Middlebury College 29-33
50 University of Rochester 29-33