I am not sure if I am reading too much into this or if I am just compleatly wrong, but from what I understand you can put characters in units and units within units and this is why: The rules state “Models fight in units. A unit can have one or more models, but cannot include models that use different warscrolls. A unit must be set up and finish any sort of move as a single group of models, with all models within 1" of at least one other model from their unit. If anything causes a unit to become split up during a battle, it must reform the next time that it moves” Excerpt From: “AoS Rules EPUB Phone.” iBooks. This material may be protected by copyright. So basically you cant have a unit that is composed of multiple warscrolls. For that I understand that you cant have a mix of miniatures from diferent warscrolls and consider all models to be equal for the purposes of determining the 1" from friendly models in the same warscroll. You can however, place a unit or hero and than sorrownd it with models of a different warscroll as long as all models from the individial warscrolls are within one inch of any model within the warscroll. This is possible since there is no restrinction about how far/close can friendly warscrolls be apart. And this would alow you to ultimately place heros or units within other units, you would still be able to shoot them or cast magic at them but you would be able to some how protec those units
I think this is pretty valid as far as I can tell. I like the idea of having my Slann sitting in a ring or a U shaped unit of temple guard. It would help maintain the aesthetic of the old Slann/TG relationship and protect your Slann from being stuck in assaults he doesn't want to be in. Good find!
So basically you can place models from other units block true line of sight and thus protect your characters. It does work to a certain extent. The only problems you'll have is when those units move separately the character won't be able to remain in the centre unless it can fly (ie. slaan) and can keep up with the protecting unit. The only problem I find is with catapult style artillery. Often these war machines need no line of sight. Without look out sir it really seems to be the best way to protect those buffing and spell casting heroes.
The difference would be in the charging/combat phase. If the other army has no shooting and no artillery, you are golden. They have to go through the unit to get to the hero. This will not protect the hero from shooting or magic however. If they concentrate fire on the hero, the hero is gone! The unit can’t do anything. Might as well place the hero behind the unit, it does almost the same thing provided they don’t have units with an ability like the chameleons.
Another thing to add to Kultak's response is that if your unit has formed a circle around your hero then in the combat phase they wouldn't all be able to reach with the pile in move as some would be at the back about 4-6 inches from the battle line. The enemy would have a major advantage in the combat phase if they could maximise models in range.
Hmm, I think that if you are careful with movements you should be able to have a character tagged on the back of a unit who "just happens" to move around with them. Re the slann problem, I dunno. Maybe leaving the slann @ the back of the unit and accepting that he cant stay as part of it forever?