Shizuoka Cicada(Lang) - Help

[ShizzyCic]

Diagrams in Tanteidan Magazine 84. I have a feeling I just have layers ordered incorrectly and it is frustrating me... Any help is appreciated.

Trouble is at step 30. I know the motion, seeing as when I first got stuck I skipped it and sunk the back in step 31. Any help on this step would be very great.

P.S. Is step 19 an open or closed sink? Same for the sinking in step 31, I first did open, but am unsure if they should be closed.

Thanks

[ShizzyCic]

Nevermind, finished the cicada. :]

[Mars]

I would greatly appreciate help with step 20. Locating the four corners is no problem, but when it comes to reverse folding any of them, I'm clueless of to how to when the previous sinking (from step 19) gets in the way.

Edit: Figured it out, but not on step 20. After I did all the sink folds after step 20, I found it easier to sink those pesky corners.