Glen and Adam,
I spent some time considering this thorny problem several years ago and eventually worked it out.
What you must remember is that Greener, Davidson and Sowerby were masters of modifying what came out of the mould. In particular it is difficult to find any examples of Davidson cloud glass that have not been modified in some way post-moulding. For example the 34 pattern comprised everything from a low bowl with a recurved rim, through deep bowls, vases, to a lamp base - all from the same mould!
The 279 "Column" vase has a mould join about 90% of the way up the vase along the top of the nine side panels. So the plain rim was moulded by the plunger, not the three side sections. To extract it from the mould the rim had to be vertical and tapered. The vase would have been pushed onto a conical former to obtain the standard 279 shape, and on to a trough shaped former to obtain the 279D shape.
Back to your basket. Had the basket been moulded as a bowl shape, the two sides of the mould would have had to been lifted out, not pulled apart sideways. The underside of the top of the handle would have been wedge-shaped to match this angle. But the underside of the top of the handle is rounded, not wedge shaped. So the two sides of the mould must have been pulled directly apart, not at an angle. Hence the bowl must have been flat. QED.
The creation of the round or wavy bowl shape must have been post moulding, quickly done while the glass was still plastic. Presumably the basket was pushed or just dropped into an appropriate wavy or plain bowl-shaped former. You can see the evidence for this as there is always a depression on the outside opposite the inside of the handle, where the thicker glass of the handle resisted the change and pulled the glass away from the former.
Supreme masters of this technique were PV and MW, back in the Victorian era. Just look at Thompson, p50, the cruet bottle on the right. The bottle is pressed glass. It must have left the mould with a long, slightly thinning tubular extension to provide enough metal to work into the neck and rim. The shoulder panels are cut. The stopper was completely hand made and cut. Fabulous! I have such a cruet set in stock and a pickle jar from each glassworks. They are simply mindblowing!
I await Adam's comments with some trepidation.