the 'pipe fill' bears derating,
30A(T310-16) x 45%(T310-15(b)(2))= 13.5A,
so next 240-6 would be 15A
the 'jb' needs only to meet fill requirements. As the wires have been cut, instead of passing thru, i beleive your fill requirements are doubled.
21 x 2.25= 47+ cubes
42 x 2.25= 94.5 cubes