My first try was in forge, freezed at 5.5k/10k of the 19th wave, I was a little mad but hey, I knew it could happend ...
Second try yesterday, in alchemy, got to 20 on hard.
(As soon as it ended, I sold some tower to make it end so it saved my score and I got 6th place on the leaderboard)
Also, can't say that it helped, but near the end, i took 30/45 minutes breaks between waves. The killing thing on the bottom right seemed to be taking almost a wave behind of the actual killing. I tought that it might help to let it "process" all this information. But it's pure speculation ...
Sorry for the mistakes, english is not my first language.