Good questions ... we're in exactly the same position.

My threshold is about 1 inch higher than the wood floor of the hallway. Then it has a slight "ramp" to the middle of the threshold. At that point it becomes level and it the same level as the tile floor.

Mine spans the entire door frame and is only as wide as the frame, about 4.5 inches for me.

I believe the ramp-edge type threshold is called a Hollywood bevel (?). We should've had them do this on the saddle for our hall bathroom, but didn't. The saddle sits higher than the HW floor in the hallway outside the bathroom. I keep saying I'll have to put a "watch your step" sign by the doorway when we have guests over! :-)

Thanks for your responses. If I understand correctly, the bevel is only on one side? (I have seen prefab saddles/thresholds that are beveled on both sides.) How is the underside addressed? Is it notched somehow to accomodate the higher floor? Or is it set at an angle to span the two floors? How thick does it need to be in order to not crack? Help!

The underlayment for the tile floor extends out to the wood floor. The threshold is placed on top of this.

Yes, the bevel is only on one side. Here is a picture of mine that I hope will help. Please excuse the unfinished wood floor -- it's next on the list of to-do's.

As you can see, the light reflects only on the flat part of the threshold, so you can see where the bevel ends. The white part just above the wood floor is the tile underlayment. I am sure there are others on this board who are far more familiar with this process and can fill in the blanks for you.

I had this issue and I made slanting hardwood bevels for my tile to wood transistion. Smooth on both sides with no banging of toes. I will post pics. we went with almost the entire doorframe.
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It depends on the AMOUNT of difference in elevation as to how the threshold should be installed, also with reference to which bevel type it should be (standard vs. handicapped, AKA hollywood). As for where in the doorway it should be, it should start under the door (if it's up to me, it should abutt the tile flush with the inside face of the door), and project out from there.

Here is a link that might be useful: look partway down the page for bevel types