If copy_to is used to combine multiple string fields, should it concatenate them together?

I want to combine "make" and "model" fields for a vehicle. For example, I would like "Nissan" and "Ultima" become "Nissan Ultima".

When I use copy_to to create a make_model field at index time, it is pushing the contents into an array instead of concatenating the strings together. It looks like this:
"make_model.label": [
"Nissan",
"Altima"
]

Is this the expected behavior? Is there a better way to accomplish this other than generating this field manually ahead of time?

Also, is there a way to enforce the order that copy_to performs? I noticed that it seems to respect the json that I provide it with over the order that it is defined in the mapping.

Thanks!