- Your steam box is too hot and will drive moisture OUT of the wood. The point of using steam is to keep the wood at ~212 F. That's why boiling also works well for bending wood.

- If your ribs are only 1/4" thick, 3-4 minutes of steaming is as much as they will need. Excessive time will dry out the wood and increase the likelihood of breakage.

- Soaking is unnecessary with green or air-dried wood.

It's great that you had the success that you did, but it may actually have been in spite of the methods you used, rather than because of them.