Yes, you have to install it up there.
You may use that technique to install it under the head on a palm to come down.
Both eucs and large ficus have long straight leaders. In one case we were doing a crane job and the central leader which was going to be craned out last had a dying top. So the FS was installed on the straight stem under the "dodgey" wood.
Last pic was that section, secure crane, abseil down to cutting postion, remove FS, wella.
Imagine on a tall euc TD, you might be able to fell the head half way up but need to remove some other branches etc. You could install the FS on the straight stem, do the rest of your work then drop the head out.
It's just another thing to keep in mind, you may not be able to shoot a decent high point, rope too short, dont need to go that high etc so keep it in mind that you can use this technique.