Some cats go outside and dont wanna go inside , others are the reverse and most like a half and half affair
I have four cats and a big garden, one cat goes outside no matter what the weather and it would only be a person or another cat who would scare here abnd she would come back in.
One cat only goes inside and the other two are inside.outside ones!
You cant train them to go only outside cos there are too many things that may go wrong, weather, a visiting cat, scared of something etc etc and even if they always seem to go outside you still need an indoor tray or two just in case.
I have three indoor trays too and only one is used regularily , another only occaisonally and the third nearly never
In the summer the two are usually never touched but in the winter used more.