How full does the reservoir have to be for their tongues to reach the sugar water?

I wondered the same thing, so I put one cup of sugar water in the feeder and watched. Hummers have really long tongues! When I fill the feeder up the bugs get in the sugar water and it looks awful and the holes they drink from seem to get mildewy before the feeder is empty. So, now I put 1 1/2 cups in the feeder once a week and then clean it good before refilling. That's what works for me. Hope this helps.

will humming birds eat from this if you set it on a table, rather than hanging it?

I'm guessing, but I would think not. They seem to hover near it before alighting on the little rim for them to perch on, and I don't think that they could hover efficiently if the feeder were sitting on a table. The can't land on your table and walk over to the feeder, as their legs are so fragile that they can sit/perch on them, but not walk on them.

can you put grape jelly in this feeder?

The top of the feeder comes off it just sits there and it would very easy to fill with nectar or grape jelly.

This feeder seems designed for larger hummingbirds with long beaks.(?)

I've seen both the larger and smaller varieties of hummingbirds use this feeder. The little guys are migratory in my area and prefer my flowers. My sister has these feeders also and both the larger and smaller hummingbirds use them.

2 Pack 16 OZ Hummingbird Feeders for Outdoor 5 Feeder Ports Ant Bee Proof Leak-Proof Cleaning Brushes Nectar Easy Clean Fill Bird Feeder for Garden Red Décor for Mom

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