Thank you, bossyvossy! I'll do that, and go ahead and move them :)

Not sure I would assign shade the reason for slow growth - nandina is extremely shade tolerant. In fact it is a shrub recommended for dry shade, a rather tricky gardening situation!!

Moving from shade to full sun is a bit of a severe shift. And if you check the literature, nandina grown in hot climates is best shielded from the afternoon sun.

Ok, yes they'd get some afternoon sun. I have them all along a certain bed, and the ones that get a few hours of sun are big and full and the ones that don't get any don't grow. I have a few others scattered around too, and the ones with more sun are prettier. I think I'd still like them in a spot that gets some sun, but maybe I do need to wait and find a spot without the afternoon sun...

I've been seeing plenty of west-facing nandinas in my neighborhood, and they look great. So I'm still going to move them to a sunnier spot.

We've had n. compactas do very well in full sun until mid-afternoon, full sun from mid-afternoon, and just morning sun in an eastern exposure. Believe the bit of shade does help them get through the north Texas Aug/Sep heat with little supplemental water. Tough plants, so might be fine with a full day of sun in an irrigated spot. The only nandina we've had succumb to our heat was an ignored 'Gulf Stream' dwarf getting full afternoon sun on a west facing fence in a sloped unirrigated bed - though not sure the dwarf lines are quite as robust as the compactas and standards.

The two n. compactas on our east wall are now topped out at about 7 ft after ~18 years. However most of that time, the one shaded by oaks remained 1 to 2 ft shorter than the one getting full morning sun. The standard n. domestica that came with the house reached their terminal height (~9 ft) in full shade by something close to 20 years. So they're capable of eventually reaching full size even in heavy shade, but can get there much faster with a bit more light.... plus the color is usually somewhat better.

When you transplant, don't give up on them too soon. We've divided and moved n. domesticas/compactas all around our lot. Depending on the timing, they may drop all their leaves and not leaf out again until the following spring.