### 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_
{
    return RPCHelpMan{"sendtoaddress",
                "\nSend an amount to a given address." +
        HELP_REQUIRING_PASSPHRASE,
                {
                    {"address", RPCArg::Type::STR, RPCArg::Optional::NO, "The bitcoin address to send to."},
                    {"amount", RPCArg::Type::AMOUNT, RPCArg::Optional::NO, "The amount in " + CURRENCY_UNIT + " to send. eg 0.1"},
                    {"comment", RPCArg::Type::STR, RPCArg::Optional::OMITTED, "A comment used to store what the transaction is for.\n"
                                         "This is not part of the transaction, just kept in your wallet."},
                    {"comment_to", RPCArg::Type::STR, RPCArg::Optional::OMITTED, "A comment to store the name of the person or organization\n"
                                         "to which you're sending the transaction. This is not part of the \n"
                                         "transaction, just kept in your wallet."},
                    {"subtractfeefromamount", RPCArg::Type::BOOL, RPCArg::Default{false}, "The fee will be deducted from the amount being sent.\n"
                                         "The recipient will receive less bitcoins than you enter in the amount field."},
                    {"replaceable", RPCArg::Type::BOOL, RPCArg::DefaultHint{"wallet default"}, "Signal that this transaction can be replaced by a transaction (BIP 125)"},
                    {"conf_target", RPCArg::Type::NUM, RPCArg::DefaultHint{"wallet -txconfirmtarget"}, "Confirmation target in blocks"},
                    {"estimate_mode", RPCArg::Type::STR, RPCArg::Default{"unset"}, "The fee estimate mode, must be one of (case insensitive):\n"
                     "\"" + FeeModes("\"\n\"") + "\""},
                    {"avoid_reuse", RPCArg::Type::BOOL, RPCArg::Default{true}, "(only available if avoid_reuse wallet flag is set) Avoid spending from dirty addresses; addresses are considered\n"
                                         "dirty if they have previously been used in a transaction. If true, this also activates avoidpartialspends, grouping outputs by their addresses."},
                    {"fee_rate", RPCArg::Type::AMOUNT, RPCArg::DefaultHint{"not set, fall back to wallet fee estimation"}, "Specify a fee rate in " + CURRENCY_ATOM + "/vB."},
                    {"verbose", RPCArg::Type::BOOL, RPCArg::Default{false}, "If true, return extra information about the transaction."},
                },
                {
                    RPCResult{"if verbose is not set or set to false",
                        RPCResult::Type::STR_HEX, "txid", "The transaction id."
                    },
                    RPCResult{"if verbose is set to true",
                        RPCResult::Type::OBJ, "", "",
                        {