I bought Tier 7 twice but once I got to 20000 miles I still had 24 sigils left, meaning I wasted 500 gems…
EDIT: 164 matches to get there
I always took the highest miles except for few times when the other match gave a stat boost.
Then again I had luck to only lose a Valraven once when one appeared in a boss fight and the AI’s Chalcedony killed my whole team in one turn.
Yes, that means AI casting Chalcedony with three constructs will give Chalcedony infinite mana and extra turns despite player team being unable to do that with four constructs.