Original:
Classic Spanish Sangria Recipe

    1 750 ml bottle of red wine (a medium bodied red wine like Garnacha, Merlot or Tempranillo)
    1 cup soda water or Cava (Spanish Champagne) to top off
    ¼ – ½ cup sugar
    Juice from 1 orange or 1 lemon or 2 limes
    lime wheels for garnish

(From http://winefolly.com/tutorial/search-best-sangria-recipe/)

Scaled to 2/3rds:
500ml red wine
2/3rds cup soda water
1/8 cup sugar (and a drop or two of stevia?) (not all dissolved)
juice from one lemon, one lime, save wheels from each for garnish

results: fills two tall glasses on ice, about 250ml of wine each.  tastes like sangria to me.


Try 2:

500 ml red wine
1 cup soda water
1/4 scant cup sugar
1 jigger ginger syrup
juice from:
 1 orange
 1 lemon
 1 lime
save a ring from each for garnish, served over ice.

results:
sweeter than try 1, due to ginger syrup sugar and orange juice, but also good.  could stand even more ginger, possibly just 3 jiggers of syrup and no granulated sugar.