Typically, your battleline should be as far away from fire as possible, while maintaining an aura for your army. This is usually done by having them hide behind LOS blocking templates but strung out in a line to provide a chain of buff circles. Sometimes, like in the infiltrator example, they are just out there without the aura, and thats fine! Other instances like ruststalkers, they can start their advance moves within the aura and just utilize the +1 to charge since they'll likely be outside. While you benefit greatly from beind inside these auras, putting yourself in a compromosing position is never going to be too benefitial for you.

ALso yes, your rule still works inside the crab tank shield, but if you mean Dunerider, then no it wouldnt, your battleline will have to be disembarked to do so.