That feeding methods is used to wake up colony in spring that they start brooding. But it is December now.
I do not even ask what is idea. It is a disaster, not even idea.
"big hives try to rob mating nucs" - you should understand that you you self invite them to do that. Don't do that in winter, and not at all in summer.
"open feeding trials before permanent snowfalls" -- somebody told you to do so....
When you give open honey to the hive, questions is not that "bees like it". No, they wonder what is wrong, because somebody has broken they honey stores. They are more upset than happy. What they will do; they start to rearrange their stores so that food is in cells and not allaround corners.
What do you think that someone comes to you home and throws tomatoes, juice and bread onto walls?
A years ago I give to hives old capped honey frames for winter food. Frames seemed good, but it took one week that bees arranged the frames and calmed to cluster again. Bees cleaned broken cells, moved food and tried to recap food in low temperature.