What is the acceptable vanilla:vodka range for homemade vanilla extract? I am extremely bad at getting the seeds out of my vanilla beans. So I started putting the "used" beans (which still have at least 1/3 of their seeds) in a small jar with some vodka, and using the liquid as "neverending vanilla extract". 

There are recipes for vanilla extract out there, but they assume that one would put an exact amount of vanilla beans and vodka together once, then wait, so they give a single ratio. I can't meet this ratio always, but I want to know what the acceptable range is. So: 


what is the lower bound of vanilla per ml of vodka so that below that bound, the extract will give a baking good more of a vodka taste than a vanilla taste? 
what is the upper bound of vanilla per ml of vodka so that above that bound, the aroma isn't getting extracted due to oversaturation? 


I want to know these bounds so I can adjust the vodka a bit whenever I add more vanilla beans.
According to this recipe, the federally mandated minimum is 0.8 oz per cup - the recipe recommends at least 1 oz per cup for anyone who isn't extracting it with industrial equipment, or about 30g of vanilla bean per 250mL of vodka.

There isn't an upper bound given, but while I have seen "double-strength" extracts containing twice the vanilla, I haven't seen anything stronger, so I would say 60g per 250mL alcohol would be a reasonable upper limit.