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...
Best,
EW