I believe Ed's trash to stash recommends about 1 oz dry cannabis / Liter of booze. IMO Everclear is the worst thing to use as it is so high in alcohol that it strips lots of chlorophyll out in addition to active compounds, plus everclear in itself is VERY harsh for the end user. I have never thought to add agave, I have some everclear tincture just sitting around because it makes my mouth so raw when it is applied, no bueno. I will try this, Danks a lot lampworker! Agave is great as a flush carb too, it dilutes in water very easily compared to some other substitutes.
I like 1 oz dank med / Liter of High Quality BRANDY, the smoothest alcohol tinctures I have used were made by my father (my tincture guru) out of Brandy. He has tried rum (lots of impurities), everclear (IMO way too harsh for direct spray use), brandy (the smoothest). Cold and slow are the key to good tincture he says.
Also I have learned that a fine mist under the tongue seems to aid absorption and increase effectiveness. I would do a spray top instead of a dropper personally. Also, warn your patients that after use it will smell like they took a shot of whatever booze you go with!