system
Given the following post, respond as if you're commenting on Reddit:
human
[Marvel] Why does Ant-man retain absolute strength when shrinking but not when growing?

When Ant-man shrinks down, he essentially has super strength because his strength doesn't decrease proportionally to his size. But when growing, his strength increases proportionally to his size. (ie, he can lift 100 pounds when human or ant sized, but much more when giant sized.)
gpt
I think, and this might not be canon anymore, that when Hank Pym shrinks, he isn't just losing mass, but also compressing the space between atoms, making himself much more dense. That extra density is what gives him his super strength in ant form.

When he grows, he's actually adding additional mass from an alternate dimension, similar to how the Hulk grows larger and Wolverine heals massive wounds. That additional muscle mass provides extra power when in giant form.