You can add a 4-6" wide trim board to fill the space between ceiling and window frame. Then your Roman shade can be mounted anywhere on that board. If you are buying a ready-made shade, adjust the height to let it end an inch or so above the window sill to minimize splashes.

If daytime privacy is a concern, consider adding one or two short tiers of sheer curtains on tension rods.

I would hang it from just above the window frame.

you said you have to do an inside mount, sounds like outside.

Hang it just under the ceiling, if it's attractive, it will look great!

What lisedv said.

You do not hang a roman shade that is measured for inside mount on the outside of the frame. You need to measure the width needed to hang a shade that will cover the outside frame, as lisedv shows.

Just read you post again. You say it's too shallow for an inside mount but still want to do that?

Ope! sorry OUTSIDE mount how close to ceiling shouldni hang it? ?

I figured that was a typo. Hang it between the top of the window casing and the ceiling.

Do you want it to be operable or just for decoration? Is it ready made or custom?

Operable… custom made

In that case your fabricator and installer should determine the exact placement. And it will depend on what brackets are being used and where the studs are.