Probably there are more stick temp-resistant powders than spherical, but there are also a bunch of sphericals, some of which aren't advertised as temp-resistant. One is Ramshot Big Game, which in my testing over the years in a lot of different cartridges has proven as temp-resistant as any of the Hodgdon Extremes.
I don't know much about the technical aspects of producing temp-resistant powders, because powder companies understandably tend to be very reticent to discuss their manufacturing techniques, especially to gun writers who might write about them publicly.
But did indirectly hear of one technique, from a powder distributor who'd visited a major powder factory. The folks there told him that flattening the granules of spherical powders (which they called "laminating") made them more temp-resistant--but also less accurate.
