Your math isn't working because you're comparing the weight of the two parts, not the volume. The two have different weights because their mass is different. Volume, how much space they take up, is what matters here.
I've only been working in small amounts, but I use the Great Planes epoxy cups from Hobby Town. They have graduations in different units, ounces, drams, ccs etc. It doesn't matter which you use, just whichever gives you the amount you need. (In this case ounces probably refers to the weight of water. But that doesn't matter, you can use the markings as a volume unit.) If you need a large amount just use the whole cup, 1 cup of A and 4 cups of B.
For my phaser build I'm using EpoxAmite laminating epoxy. It has a mix ratio by weight of 100A:29B, but by volume it's 3A:1B. Working in very small amounts made measuring by weight difficult, so I use volume (I wish all products had mix by volume directions!). I just pour out 3 drams of A and 1 dram of B.