I want to build on this a little bit, because there is a mirrored design here that I think is important to address.
People don't like rolling the maximum result leading to the die downgrading. They feel it takes away from the "joy" of rolling a high number. But, there is only one other place in the design to put the downgrade, and that is rolling the lowest number, which I feel is worse.
To throw out some quick examples involving the Psi Knight using their damage shield, 1d6 and can upgrade.
Current Rules:
You roll a 6. You have blocked the maximum amount of damage, but your die drops to a d4 for next round.
You roll a 1. You have blocked the minimum amount of damage, but you die upgrades to a d8 for next round.
My use of "but" here is important. The two sides of the sentence are opposed. One is a "good" thing the other a "bad" thing.
Mirrored rules:
You roll a 6. You have blocked the maximum amount of damage, and your die upgrades to a d8 for next round.
You roll a 1. You have blocked the minimum amount of damage, and your die drops to a d4 for next round.
And here we have higher highs, but also lower lows. You failed to make an impact and weakened yourself in the process. That feels far worse than making the biggest impact possible and then weakening yourself.
This is why I like the Psi Die design, very few mechanics work to make rolling 1's suck less. I mean, how many times have you seen a battlemaster roll that die and get a 1? Or roll a 1 on bless when it was the only number that wouldn't help? 1's are feel bad numbers in the game, and this takes them and gives you a boost when you get them.