The classic proportions for a Between the Sheets are most often quoted as being:
30ml (1oz) Light rum
30ml (1oz) Cognac brandy
30ml (1oz) Triple sec...
Impressive amount of research! I see a Jamaican rum version in the comments, which is worth noting. J.A. Groshusko's 1933 Jack's Manual uses Jamaican rum.
I followed Ander's recipe and used 22.5ml brandy, 22.5ml Havana Club 3, 30ml dry curacao, and 15ml lemon juice. Then add 10ml of demerara syrup and it tasted much bater.
I followed the recipe and it was good, albeit a bit mild. The second time I made it I used gold rum and it was much more to my liking, a bit more boozy.
Made it exactly like this and it absolutely works. It is really all about what you use. The Cognac comes through first. The rum choice is even more important, where if you use a charcoal filtered rum, that's probably where there is this 'cancelling' occurring. I used Havana Club 3, and I get the rum. The slight sherbet-y sweetness comes from the Triple Sec combined with the tiny sourness of the lemon. It works very well.
I feel like the Cognac and rum really cancel themselves out so I am only left with a sweat hard lemonade, which is something I could achieve with just vodka and lemonade. Maybe I am just not a fan of split base drinks but I feel like a cocktail should be showing off just one spirit.