I find it much harder to play piano after harp because the spacing is so much wider. Harpsichord, on the other hand, is about the same as the harp, so the keys are very comfortable to play. I think the degree of difficulty in switching from piano to harp probably depends on the type of piano technique you were taught. But I do notice a lot of harpists who are excellent pianists have the habit of not closing their fingers, which is to me an impedance.