The attack damage % used by Shield Wall is derived explicitly from the base off hand physical damage inherent to the gem itself. No amount of damage on a weapon in the main hand will contribute to Shield Wall damage.
Focusing on the Armour value on your shield is one of the methods for scaling Shield Wall damage.
Passive tree nodes that contain the text X% increased Defences from Equipped Shield such as Towering Shield, Core of the Guardian, Spiked Shield, and Flashy Deflection do not impact Shield Wall damage. Instead, they impact the final Armour value added to the player rather than the implicit Armour value of the shield itself.
Gem level progression
Level
Mana Cost
Attack Damage
1
0
0
13
65%
2
3
9
15
71%
3
6
14
18
79%
4
10
21
20
86%
5
14
28
23
93%
6
18
35
25
100%
7
22
41
28
108%
8
26
48
32
115%
9
31
57
35
121%
10
36
65
39
128%
11
41
74
43
136%
12
46
82
47
144%
13
52
92
51
153%
14
58
103
56
162%
15
64
113
61
172%
16
66
116
66
183%
17
72
126
72
195%
18
78
137
78
207%
19
84
147
85
221%
20
90
157
92
235%
Recommended support gems
The following support gems are recommendations by GGG as listed in-game, and do not necessarily reflect optimal combinations or the views of the wiki.
Gem tier
Support gems
I
II
III
IV
V
Item acquisition
Shield Wall has restrictions on where or how it can drop.
