Slow and boring is a good summary.
To amend my earlier complaint, I fought 4 battles to get back on leaderboard, and a raven replaced the Spirit Fox twice. So at least that happened. 
And thanks to the two suggestions for leftover sigils, @AMT and @Jonathan. I hadn’t considered doing that before. 
Whew, that was close. I went Tier V and 22x multiplier (used hero), and finished with 3 sigils left.
I’ve reached all rewards on several Bounty events (including current one) with Tier IV and x26 multiplier. It just required to win all battles without missed valravens or if you miss 1 valraven or loss up to 2 battles you need the last valraven to spawn at the beginning of his possible range and not at the end.