How does EIP-1559 adjust basefee if ETH price goes up or down?

My understanding of EIP-1559 is that if a block is 50% full then the basefee doesn't change. If it's above or below the 50% then it goes up or down as well. But what if blocks remain 50% full and ETH price keeps going up? If the basefee remains the same, the USD value of that basefee will go up.

My initial thought was that, if ETH price went up, then less people will want to pay for the now higher basefee with respect to USD so blocks will end up less than 50% full and basefee falls, but the problem I can't get my head around is this means that blocks would also contain less transactions/gas which means that if we wanted to support # of transactions at 50% we would be forced to pay high basefees in terms of USD.

As an example:

ETH price = $2k

Block at 50% = 12.5 Million Gas

Basefee = 100 gwei

Simple ETH transfer = $4.20

— Eth goes up —

ETH price = $2,500

Block % Drops = 10 Million Gas

Basefee = 80 Gwei

Simple ETH transfer = $4.20

— If we wanted to support 12.5 M Gas Blocks, we are forced to pay more USD since basefee stays the same!

ETH price = $2,500

Block at 50% = 12.5 Million Gas

Basefee = 100 Gwei

Simple ETH transfer = $5.25

Under the current auction system, when ETH price goes up, the gas price (typically goes down) to attempt to match the same USD value:

ETH price = $2,500

Block full at 12.5 M Gas

Gas price = 80 Gwei

Simple ETH transfer = $4.20

How does EIP-1559 keep basefee relative to USD if it's purely based on block capacity?