Can't stay in tier 20?

Really? I thought the cutoff was in the high 720's, so a 732 should just barely be enough. Unless you are getting a lot of low ball scores of course. I hate it when that happens. If your max is 732 it is possible your 5 match average is in the mid to low 720's which would make you miss the cut off.

If you fish and get all matches as max do you still miss? Also,are using blessings, yes? Blessings are important for score inflation. My score jumps something like 10 points during fire season(that is my best season).Makes it a heck of a lot easier to hit cutoffs.

You also have to keep in mind the cost of their other skills, namely the passives in A B C and S, try using skills that cost 240 in every slot, upgrade skills like QR2 to the third level and avoid seal like atk+3 or Quickened pulse since they score much less compared to other seals like DIstant Def.
My core is formed by Eirika, Nowi and Nino all of them are +10 and i have rally def/res on Eirika, all of them have Aether and Eirika and Nowi skills all cost 240 SP, exept for DC on Eirika which costs 300sp and i have no problem staying in tier20.

You can also give an AoE special to your bonus hero, this will increase your score since they cost more than specials like Bonfire

Max out your passives and seals with 240SP slots, give an AoE (300 SP) or a 500 SP slot for the special on your units, and you should be a lot better off. Refining regular weapons also adds 50 SP, and give the others a dual rally. My core has a single maxed unit and some mid-level merge count units, and I score in the mid to upper 730s and have been staying T20 for the last month now. You shouldn’t have an issue if you do those things and make one final run at it, and don’t be afraid to walk away from an offering of 730 or below. Dueling crests are easy to come by.

The past 3 water seasons have seen cutoffs around 3662, 3670, 3650, and this week will probably be close to 3654 or 3656 based on how the second arena week always scores higher than the first for a rotation.

720 was enough with 7 perfect rounds but with the change to 5 rounds 730 just scrapes by some weeks. I can only stay in if I'm lucky enough to have a merged bonus hero.