Even 18% seems low for overall. Considering the mix of pools. Tri take is 25% isn't it? It's usually as big as the WPS or exacta pool.
Close enough for government work.
In IL, it's 17/20.5/25 -- blended take normally falls somewhere around 21-21.5'ish.
For the BigM, it's 17/19/25, with 15 on P3s, Supers, and the P4. Not really sure of the pool ratios, but you could easily figure out the blended take if you really felt the need...