>I think, the proportion of sugar to water in the feeding syrup is by weigh not volume
Whatever the cause of the coincidence, a pint of sugar weighs a pound. A pint of water weighs a pound. It matters not one whit if you go by weight or volume or even mix the two. Since sugar comes in packages that are weighed by the pound and since water is easily measured by volume, I just put a pint of water in for every 2 pounds of sugar. If the package of sugar is opened and I don't know how much is there, I'll put a a pint of water for every 2 pints of sugar. If I had a scale, I could just as easily put a pound of water in for every two pounds of sugar.
It's all the same.
This is NOT true for all solids and liquids, of course. Just for sugar and water.