Mikey, I winter feed my bees differently. I have found that the heft test isn't always reliable, because once you find that the hive is light, the bees have possibly already run out of food, and they can die within 4 days without food. After all you never know when something in life happens to you and you can't get out to your hives for the heft test.
I give the bees a second source of food on the inner covers with a shim/spacer, then the lid on top. I never let this food run out, EVER! They can dine on the honey on the frames, or they can go to the buffet of food upstairs.
Last winter I kept 14 hives alive all winter with this method. All's I have to do is lift the lid for a quick peek and add more food if needed.