I think that is right, for these games it was-
1990 we had 35,000 (total att:72,873) vs Sunderland
1993 we had 34,000 (total att:73,802) vs Leicester
2010 we had 32,000 (total att:73,108) vs Millwall
2012 we had 30,000 (total att:49,602) vs Chesterfield
2015 we had 20,100 (total att:48,236) vs Preston
Massive asterisk vs Preston with all the travel disruptions we had and losing twice in recent years.
I think we're far enough away not from those games that we'd probably take well over 30k again.