Hi harvey--I'm new, too, but I've been told it's best to feed bees INside the hive. Feeding OUTside encourages robbing by other colonies. Do you have a way of installing a feeder inside the hive? I have a Boardman with a Mason jar tucked in the back of my hive (topbar) and I know there a feeders specific to Langstroth hives.
Maybe your bees have enough of the real stuff around that they don't need to be fed! Can you see them coming back with pollen loaded on their legs?
A boardman feeder is a good way to attract robber bees since it places the syrup so close to the entrance. Putting a feeder inside of a weak hive will only slow the robbers down if they are determined. But feeding internally is much better than using a boardman feeder. Open feeding, in the middle of the bee yard (amidst the hives) is also a good way to induce robbing.
However, open feeding is my choice of feeding method and here's why:
1. It feeds all the hives at the same time, thereby reducing the robbing incidence as each hive is working the source not another hive.
2. The feeder is placed some distance from the bee yard (hives) so that the bees see it as a nectar source, mimicking foraging.
3. It is easier to check and refill the feeders without disturbing the hives.
4. It works even during dearths when robbing is more of probability because of #1 & #2.
I use inverted gallon paint cans or large jars with holes poked in the lids so the bees have to take the syrup as if foraging. If I were to feed my hives at the moment I would set up my feeding station at the edge of the blackberry vines that grow at one end of the pasture.
the further the feeding station from the bees the better it works and the more it mimics actual foraging the better it works.