EIP-2929: Gas cost increases for state access opcodes

[axic]

From the specification:

When an address is either the target of a ( EXTCODESIZE ( 0x3B ), EXTCODECOPY ( 0x3C ), EXTCODEHASH ( 0x3F ) or BALANCE ( 0x31 )) opcode or the target of a ( CALL ( 0xF1 ), CALLCODE ( 0xF2 ), DELEGATECALL ( 0xF4 ), STATICCALL ( 0xFA )) opcode, the gas costs are computed as follows:

• If the target is not in accessed_addresses , charge COLD_ACCOUNT_ACCESS_COST gas, and add the address to accessed_addresses .
• Otherwise, charge WARM_STORAGE_READ_COST gas.

It is unclear to me whether the above is a cost on top of the current cost or replacing it. For EXTCODESIZE, etc. it seems to be replacing, but for CALLs I believe it may only be replacing the base cost? Can this be clarified further?