What would be the appropriate amount to tip on a $135 for good service at a Sushi place? ?

Since the lock down, when a majority of servers were without income, I have been doing a 20% gratuity, even at buffets. These people need to recover, and I'm sure the government checks don't even start to make up for lost income.

Why are you trying to complicate a basically simple situation?

If the service was good, the person paying calculates 15-20% of the total, and pays it.If the service wasn't so good, you calculate 10%, and if it was really bad you don't tip at all.

But it's not the same service. The waiter is bringing out food for four people and cleaning up after four people, so it's four times the service. It doesn't matter who's paying for it all.

$20..............

You said GOOD service. So tip should be 18-20%, not 15%. That's $24.30-$27.00. 

I don't understand your idea that the tip should be less if one person pays rather then it being separate checks. I don't understand your idea that tipping at Ernie's Extra Expensive Eatery should be based on what your meal would have cost at Billy's Budget Beanery. If you want to tip 18% of $20 then you eat someplace where your meal costs $20, not at the swanky place with "the same" meal costs $50. 

i would just pay the 20.25