I have just been looking up your flash, GN of 50 (metres, ISO100)
My most powerful SB-800 GN of 38 (metres, ISO100)
Off camera flash is the way to go pointing down through a diffuser will have similar effect to on camera aimed upward diffusing off ceiling but much greater power as less loss so greater depth can be achieved.
A simple silver/white brolly can cost as little as £25 and can make a real difference.
Something for Santa?