I'm not quite sure how to respond to your scaling issue (at least without looking into it with respect to Poser's interpretation), but from my past experience, a 1.0 value and a 4.0 value should produce the exact same results.  If it's not, then it may be something specific to Poser.

re: out-of-bounds...

Yeah, UVMapper does bring up that dialog when it senses values outside the 0.0 -> 1.0 range, but you can just cancel that dialog and it's perfectly happy to deal with (display) them as expected.  I often use 'tiling' to (for example) move the Head UVs out a tile, to separate them from the Body UVs (and Transmap UVs and Mouth/Teeth UVs, etc. - each get moved out into thier own tiled space), so they aren't all piled up on top of each other (visually).  If you do that, Poser (and other apps) still work(s) fine.

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