I think the panels would need a wire more like the one Matt used on his trellis.
Gothic arched greenhouses rely on two flexible strips of
wood in tension and compression with one another through the blocks of wood glued in between them.
If wood strapping flexed the cattle panels do, they would probably be used in normal arches, without the fancy glue up.
Using fencing wire, you could force a slight bow into each cattle panel, forming something like a segment of a circle.
Zip tie them together at the top and then move their bases closer together until the cords of he segment form an accute isosceles triangle.
This
should give you the form you want, without a horozontal wire in the way