I'm avoiding looking at any of the replies so that I won't be biased (by anything other than my current knowledge and views) in giving my answer.  
 
For me the bilah starts at the ganja.  
Seeing the bilah as a representation of a kayonan or gunungan, it seems logical  that the gonjo is the root from where the rest of the blade grows or the base on which it rests.
		 
		
		
		
		
		
		
		
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