i don't understand why this is at all important, but you can at least get it right. pre-2006 system: 24 teams, one automatic from each region, with up to four bonus teams added for each region team finishing in top 16 at previous year's region. there were many years in which the west and s/se had only one representative under this system, which is one of the reasons it was changed.
IF a similar system was used with the expanded field, they'd have to extend the bonus spots to teams in the top 24. do the arithmetic.
the central region teams performed reasonably well. st. olaf finished higher than they'd been ranked all year, and grinnell finished a respectable 26th despite being one of the last (if not the absolute last) team in. st. john's finished fifth at miacs and 22nd at nationals-- not too bad. the only team that seemed to have an off race was wesleyan, and they ran without their #1 from regions.