### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current behaviour

See inline discussion at https://github.com/bitcoin/bitcoin/pull/26467#discussion_r1269177446

@whitslack:

> Consider the case where I am paying someone on chain under the stipulation that _they_ will eat the mining fee. (Thus, I specify _their_ address in `subtractfeefrom` when I'm constructing my transaction.) Later, they tell me that they can't wait for confirmation any longer and need an urgent fee bump. If I naïvely specify their output as the `reduce_output`, I may end up paying them _**much more**_ than I intended to if I only have large UTxOs in my wallet.


### Expected behaviour

Not sure.

Improving the docs is one option, but this behaviour seem quite counter intuitive.

My own suggestion:

> Should we disable the adding of new inputs when `reduce_output` is set? If someone really intends to do that, they should probably use `outputs`.

### Steps to reproduce

Haven't tried.

### Relevant log output

_No response_

### How did you obtain Bitcoin Core

Compiled from source

### What version of Bitcoin Core are you using?

Master after #26467

### Operating system and version

Any

### Machine specifications

_No response_
} else {
                CoinFilterParams coins_params;
                coins_params.min_amount = 0;
                for (const COutput& output : AvailableCoins(*pwallet, &coin_control, fee_rate, coins_params).All()) {
                    CHECK_NONFATAL(output.input_bytes > 0);
                    if (send_max && fee_rate.GetFee(output.input_bytes) > output.txout.nValue) {
                        continue;
                    }
                    CTxIn input(output.outpoint.hash, output.outpoint.n, CScript(), rbf ? MAX_BIP125_RBF_SEQUENCE : CTxIn::SEQUENCE_FINAL);
                    rawTx.vin.push_back(input);
                    total_input_value += output.txout.nValue;
                }
            }
            /
            const TxSize tx_size{CalculateMaximumSignedTxSize(CTransaction(rawTx), pwallet.get())};
            const CAmount fee_from_size{fee_rate.GetFee(tx_size.vsize)};
            const CAmount effective_value{total_input_value - fee_from_size};
            if (fee_from_size > pwallet->m_default_max_tx_fee) {
                throw JSONRPCError(RPC_WALLET_ERROR, TransactionErrorString(TransactionError::MAX_FEE_EXCEEDED).original);
            }
            if (effective_value <= 0) {
                if (send_max) {
                    throw JSONRPCError(RPC_WALLET_INSUFFICIENT_FUNDS, "Total value of UTXO pool too low to pay for transaction, try using lower feerate.");
                } else {
                    throw JSONRPCError(RPC_WALLET_INSUFFICIENT_FUNDS, "Total value of UTXO pool too low to pay for transaction. Try using lower feerate or excluding uneconomic UTXOs with 'send_max' option.");
                }
            }
            /
            if (tx_size.weight > MAX_STANDARD_TX_WEIGHT) {
                throw JSONRPCError(RPC_WALLET_ERROR, "Transaction too large.");