Upgrading the evil shoal rage ability..

[LiveInABox]

Well this is the best abilty for the swamp thing but im kinda annoying its not letting me upgrade it! whenever i get new experience its now either the armor or the spit..the armor is now really high but costs like 30 rage. I've only upgraded the shaol like twice and it stopped showing it as a choice when i choose to upgrade the armor over it, about 4 levels ago. now it never shows it.

how does it work it out what to give u as an option?