Power rune fire damage enchant not giving correct value

The axe enchant for 10% increased fire damage per 1% fire resistance above 75% is giving a fraction of the value it should

The first 2 images are the enchanted axe with about 219 fire resistance over cap which should be about 2190% increased fire damage. The second set is an axe with 73% increased fire damage. However at least on tooltip for a fire spell the damage is about the same when it should be noticeably different. Even thought this is only for the tooltip I felt the damage was low from what I had tested in POB which is why I was looking at tooltip damage and I believe there is a bug present in this enchant.