T18 Maps - How?

In previous patch, corupted maps had +1 level of area, so we could create maps T18 (T16 + irradiated + corruption)

How we can do it now if corruption doesn't give + 1 level of area?

I can see that some maps have "+ 1 to monster level of area" but they are very rare. Is there any deterministic way to enter maps T18 (area lvl 82) ?