I don't agree with that logic.
Yes, 1 bucket of a fluid is 1 block of the fluid (although it actually doesn't quite reach the top, so you could argue that is not true), but there is nothing saying 1 solid block is equivalent to 1 bucket of that material melted down.
Liquid doesn't have ingots or nuggets, so those solid conversions do not need to apply to them.
If we keep it as 1 block of a solid becomes a bucket-and-a-bit, all it means is that you don't fit an even number of blocks into your tanks. But I don't see why that is an issue, because once you have converted it to a fluid, whatever you're using it for (machines?) probably doesn't care about the solid amount.
If you want to transfer exact amounts, use the blocks. They are probably easier to transport anyway (there is a vanilla mechanic for it, and you can usually carry 64 per inventory slot as opposed to the 1 in a bucket).