Yes, I get what you are saying - but it doesn’t have anything to do with my point. I think you are getting hung up on this.
As I mentioned the seals are the best fit whether fire or chaos. The conversion is minor and distracting but is a loss for the for the pure fire build, because it would be better if they were phys->fire
However about the same amount can be gained from the amulet conversion - so the loss gain/for either is about the same.
If 100% chaos->fire and the ammy gets some %fire damage. vs 100% fire->chaos