Surface Patch on a Concave Surface?

[Anonymous]

I am trying to create a complex-curved solid from surfaces.  I was able to successfully model 5 out of 6 sides (shown here) using sketches and the top side using the patch tool.

But the final side I need (shown here)

Unlike the convex  top, I was unable to use the patch tool to create the concave bottom. Even the best surface option ended up being all wonky (See following:)

How do I get an even surface?

Thanks much.

[Anonymous]

Can you share your model to help you?

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If it was useful please give me kudos

[Anonymous]

Sorry for the omission, here is the file (I hope!)

[Anonymous]

Sorry for the late addition... see original post reply

Thanks Much