Yes Anne, bigger bezels are difficult, not only because they need more heat for the solder to flow on the back plate, but also because too much heat on the bezel strip will cause it to distort and spoil the fit.
If you are not in a position to upgrade to the whole shebang, a second torch like the one you have already could do the trick, used together one in each hand, and concentrating mostly on the backplate at first.
Other ways to reduce the heat required, is to cut a pear shaped hole in the backplate, leaving just a ledge for the stone to rest on,
Using easy solder,
And lastly using a larger refillable torch.
I have recently tried out this one from Cookson, with better results:
https://www.cooksongold.com/category...fillable+torch Dennis.
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