In practice this question doesn't apply as your fiance has been employed by the same employer for more than 6 months.
You can't answer.
Personally I think it should just be left blank.
After all Jen, you've already confirmed his annual income meets or exceeds the financial requirement in Q3.21
Either way Jen, UKVI are not going to refuse your application on that.
The confusion you feel is because these forms have been designed as 'one-size-fits-all' which results in a poorly designed form.
As long as your application complies with immigration rules all will be well.