Node spacing and Flexural reinforcement of a sheel

Hi 

I modeled a concrete shell in ram elements with applied loads at two nodes and several of supporting nodes below the shell. the purpose is to determine the amount of flexural reinforcement required. I am getting different amount of required steel based "maximum distance allowed between nodes" a finite element analysis. I used 6", 12" and 24" distance or spacing, and each spacing gave me different maximum required steel. I not sure the reason behind getting different required steel, and is there any recommendation for the node spacing?, (picture in attached).

Thanks,

Ali.

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