They may well be different, I don’t know whether they are or are not. As for “pointing the straight up” as you say, NVIS antennas are “near vertical” which means they are not pointed straight up. There is a shallow angle. NVIS antennas are also generally made with wire.
That sounds like the old system the army used. Tropo uses up gobs of power, I feel safer when it’s focused in a direction away from me.
I’ve seen a lightbulb tossed in front of a tropo dish light up and explode in a matter of seconds from the radiation hitting and converting to heat.