Good Morning, John,
One of the typical problems with flash on a TLR is that it often gets mounted above and to the side of the lenses, especially hammerhead-style units. This results in a most unattractive shadow to the side of the subject. Try to use a bracket which will put the flash directly above the lenses, so that the shadow will tend to disappear behind the subject. I had a machine shop do a custom adaptation of an existing bracket so that my Vivitar 285 could be properly positioned. I think that it's possible to purchase some brackets which will accomplish the same purpose with other types of flash units. With a TLR, the flash unit needs to be far enough forward so as not to interfere with the viewing and focusing.