Arched object will not lay flat with 4.2.1

[lil_tommy 0]

As a relative newbie, I'm having difficulty with getting an object to lay flat for slicing.  The object is arched (picture attached) and I am trying to minimize the amount of support, for both print time and material used. I have tried many different positions and this position provides the best print strength of all four possiblities.

As I rotate the object and get it close to horizontal, when I click on the "lay flat" option, the object is moved, rotated and turned into some other position. I have tried the "Auto Orientation" plug in and that does not help.

How do I get both ends to lay flat before I slice?
Thanks in advance for any help,

Tom