Incomprehensible erebus points

HI,

I do not understand erebus points calculation :

Every day, i use 2 free attempts, and i obtain 500 points. If i am a good mathematician, i thinks we win 250 points per attempt.

Today, i wanted more points for obsidian event and event collect, then i consumed 250 diams for one more attempt. (Dev. can control it on my account)

And erebus points do not progress, always 500 points.

Can you explain it ?