The diverse file extensions usually only indicate how the ROM file was dumped. Any recently dumped game will hopefully use the .sfc file extension and be header-less (FOR SNES GAMES). This is just what I like to see, and not necessarily the reality...
.fig and .swc are extensions attributed to the Super Wild Card device.
.smc indicates that the file was dumped with the Super Magic Card device.
The actual contents of the files should be similar. The fact that the patch requires a .fig extension just means that the person who made the patch may have thought the .fig dump of the ROM to be more common at the time. Normally, the only thing that effects the correct application of a patch is the existence or non-existence of a header (depending on the patch requirements). The ROM files with file extensions used by the devices I've cited above often contain extra data at the beginning of the ROM, properly referred to as a "copier header", or more commonly just called a "header".
I don't have an explanation for the file size differences since you don't give a name for the tools you've used. I'm sure the fact that the patch requires a file name extension of .fig will help someone in the future though.