I get that but if the better immune response from using two arms...

I get that but if the better immune response from using two arms is not due to chance, then it might imply, to a noob like me anyway, that the commanding officer of the body's defences is not too stressed about multiple antigen invasions at the same injection site coz the commanding officer has left entrenched more antibodies than usual in that particular site, while other antibodies move around the body telling uninformed antibodies to look out for the antigen. However, the invasion of antigens at multiple sites i.e. left AND right arm spooks the commanding officer and he has to commit even more antibodies to hang around those sites just in case there's another invasion. This leads to me wondering if that is the case, why not have the intradermal injection sites closer to where outbreaks actually occur. Why do they do deltoid area injections anyway? Is it because its closer to lymph nodes or is it simply convenience for the injector/injectee....