1 health augment heals about 10% of damage given, 2 health augments heal 15%. I probably only need one, but two just puts me over the top. Also shelling damage is fixed and only Artillery skill affects it, so other augments such as attack and affinity only affect poking, which I don't poke that much with a Wide GL
Since shelling damage is fixed and doesn't scale with raw damage, crit, or affinity, I opted to use the Rank 7 Wide LVL 4 GL for the tow augments instead of the water Rank 8 with a single augment.