For Tokina 10-17, you only need a 20mm extension with FP160 dome.
Is the extension really necessary? I expect it to sharpen the edges a little, but is it really needed?
With regard to the custom dome, the similar custom dome (FP 120-7) for the Nikon 10.5mm is truly spectacular, tho' very small. With an extension (still on order) I think that the FP 120-7 dome will work with the 10-17mm, though matching any zoom lens to a dome is a compromise if the optical centre moves during zooming. This compromise is best when the dome has a large radius, like the FP 170, but the large domes are unwieldy and often acrylic: the small domes are very handy, and optical glass. I don't have any experience with the glass FP 160 dome.
Like all Nexus gear, it's really hard to get hold of a dome or even an extension ring in Europe and the USA at the moment.
All frustrations fade away when a Nexus housing is submerged, but, oh boy, on the surface....
Tim

PS MCD (link ->) have a table of Nexus domes, but it's about 5 years out of date...