@Todd667 You're not doing anything wrong.
That will depend on the search criteria you're using.
As @Marie8425 mentioned, if you make a search for 9 guests, and both places can fit 9 guests and are compatible with other search filters you're using, they'll both appear in search results.
Then it's up to the guest whether to stay in a 1800 sqft property or in a 1200 sqft property.
I totally understand that you wouldn't want to stay with 9 people in 1200 square foot home and have to sleep in the living room.
However, you cannot judge what everybody else wants. Some other guests might wanna stay there and bargain on price for instance.
In any case, both listings (yours and the other)should show the sleeping arrangements and where the beds are located. So the guest can make an informed choice.
You can highlight in the title that your place has 4 bedrooms (for instance, you can write something like "Spacious 4-bedroom space"!