Consider for $r,c>0$ the set $$X_{r,c}=\{x \in \ell^1(\mathbb{N}) \mid \|x\|_1=r,\, \forall i \in \mathbb{N}: |x_i|<c\}.$$ Then I can show that $\inf_{x \in X_{r,c}} \|x\|_2 = 0.$ But is it possible to compute $$s_{r,c}:=\sup_{x \in X_{r,c}} \|x\|_2 \text{ ?}$$ Does at least $\lim_{c \to 0} s_{r,c}=r$ hold?