Difference in cost of leveling up 5 Stars

Just wondering if this is a bug or normal.

Black Bolt and OML are both 3/0/1 on my roster and both level 300. However to level BB up to 315 is more expensive than OML.

BB costs 38894 ISO while OML costs 37270.

Whats even stranger is one level for OML is more expensive than BB. It’s 2050 ISO to get OML to 301 and only 1966 for BB.

I thought leveling was supposed be even among the same tier.

It should even out in the end. The iso cost is not linear and it’s pretty lumpy to be honest. It when they are both at 450 it will cost same amount of iso.

I noticed this in May of last year.

https://forums.505go.com/discussion/72676/different-iso-amounts-to-level-different-5-stars#latest

That was the only post in the thread, so if you get an answer, let me know!

(As an aside, my Spider Man is now 4/1/3, Hawkeye is 4/4/2, and Ghost Rider is 4/3/1. Not much progress in a year on the classic 5-stars.)