You’re doing all the right things. 40% to 60% is ideal, but 29% is not that bad. It’s better than 5% or 8%, which is what it would be without any humidification at all. Maybe you could try hanging your laundry to dry in the harp room!
The size of the room is probably the reason the humidity isn’t higher. If the humidifier is the type that puts out ‘invisible’ humidified air(in other words, not steam or visible vapor) then you can put it right next to the harp and let it blow on the instrument. It won’t leave condensation or hurt the instrument. The humidity is going to be highest close to the humidifier, and dissipate pretty quickly as you get farther away.