You have to be in gold 1 when reset happens is all, if you get beaten down to silver before reset then you need to climb higher to prevent that. I think the safe bet is not 20 battles a week but 20 battles a day lol

Due to some interesting design decisions by Plarium, Gold1 is actually the hardest bracket to stay in, and Silver4 is the hardest bracket to advance out of.

Your best bet is to just climb past G1 - go all the way up to G5, and then just coast on 1-man defense teams.

You teams will also drop most of this the day of or even a few hours before the reset because of everyone trying to get to the tier they want. Though 20 times a week is on the very low end. Try doing 60 a week or go up a few tiers right before reset. Though I was always told if I have extra arena tokens anywhere then I'm not using the arena enough. 

G1 was hard for me, now I stay on G5 with ease. Just push