I understand that there are two situations where we may need such a knot :
A1. A mid/air binder, where we have access to both ends of our rope. When we want to bind tightly a bunch of objects, but the point where we tie the knot is not in touch with the surface of any of them, so we want our knot to remain tied and tensioned, suspended in mid air.
And/or :
A2. An binder + hitch application, where we have access to one only end of our rope. When we want to bind and pull a bunch of objects, but anticipate that we will may need to remove some of them at some time later, without untying the knot. ( or that some of them will slip off by themselves !

). However, we want our knot to hold even after this, to remain tied even if not tensioned as a binder, but as a hitch, suspended in mid air, or as fixed end-of-line loop, that will sometimes be more or less (

) "ring loaded".
Binding tightly tubes together, when we plan to be able to move them and remove some of them without untying the knot and tying / tensioning it again, is the first thing that comes to my mind, where we have a situation 2. And if the tubes are only a few, we still have a situation 1, even if we do not remove some of them - because we can not probably be sure that a knot tied on the hard surface of one tube will remain at this point later on.
We may have enough room o move our hand(s) around the point we want to / can tie our knot - or we may not. So, the possible situations are doubled ( B1 and B2). If we
do have enough room, any end-of-line bend that can be tightly tied at the first place, can possibly serve as a mid-air binder B1, and many of them also as mid-air binders + hitches B2 - because pulling them by a tail will not untie the knot. If we
do not have enough room, and we are forced to tie the knot in mid-air and tighten it only afterwards, we have to :
1. tie a noose around the object(s), tighten it and then secure it somehow.
2. tie a loop on the one end, and then pass the other end through it, pull it and tighten the knot, and then secure it, as in the previous case.
3. Tie an adjustable binder like one of the many we have been talking about the other day, and then tighten the knot by pulling the end(s) parallel to the surface of the object(s), and then secure it/them.
4....
The problem is very interesting, I believe. I do not have much experience in this kind of situations, and I can not tell right now what is the best knot of the many one can think of.
The only thing we
can not do, is to achieve this purpose by tying
two half hitches

( you will need four...) - unless you mean tying the Sheet bend, the Whatknot, or any of the four double harness bends we might consider to be interwoven half hitches. Can one manage to tie any those knots tightly enough, so they can serve as mid-air binders ?