OK, as I mentioned earlier, I am not making a toile, but am using the bodice lining to check for fit.
I tried the bodice lining on my daughter, pinning it together at the back opening. The fit was lovely across the back, and also the side front panels (the side seams sit at exactly the right places). However the fit on the front panel was a little loose, so I unpicked the tacking stitches and took in the excess on the seams of the front panel (by approx. 0.5 cm). I then checked the fit on my daughter again, and we agreed that this was fine now.
The panels had been cut out for her measurements, size 10 of the pattern. The alterations on the front panel were approximately equivalent to taking that piece down from a size 10 down to a size 6, therefore I took this piece out of the "garment" and re-cut it using the paper pattern piece, but cutting it as a size 6 (side seam only, the top edge was fine at size 10). I've also re-cut, i.e. reduced pattern piece 6 (front stay), by this amount.
It's important to note down what I've done here, so that when I cut out the bodice from the actual dress fabric I do the same thing, i.e cut pattern piece 1 at size 6, the rest of the bodice pieces at size 10, and reduce piece 6 by a small amount corresponding to the difference in size for piece 1.