We extend the analysis of [9] to the 6d (1, 0) SCFTs known as massive E-string theories, which can be engineered in massive Type IIA with 8 − n0< 8 D8-branes close to an O8− (or O8* if n0 = 8, 9). For each choice of n0 = 1, …, 9 the massive $$ {E}_{1+\left(8-{n}_0\right)} $$
E
1
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8
−
n
0
-strings (including the more exotic $$ {\overset{\sim }{E}}_1 $$
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~
1
and E0) are classified by constrained E8 Kac labels, i.e. a subset of Hom(ℤk, E8), from which one can read off the flavor subalgebra of $$ {E}_{1+\left(8-{n}_0\right)} $$
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1
+
8
−
n
0
of each SCFT. We construct hierarchies for two types of Higgs branch RG flows: flows between massive theories defined by the same n0 but different labels; flows between massive theories with different n0. These latter flows are triggered by T-brane vev’s for the right SU factor of the SCFT global symmetry, whose rank is a function of both k and n0, a situation which has so far remained vastly unexplored.