how do I make a block hover over an entity?

how do I make a block hover over an entity? but what if there is no entity under the block , then the block disappears . It does not suit me to have the block disappear and immediately appear above the entity, (I have already done this) since I have this block responsible for the redstone signal, and with such a trigger, the redstone signal flashes (if anything, I create an entity that, when standing on redstone, gives a signal to redstone ,)