Focus point for Birds in flight at a feeder

I want to set up my camera on a tripod near a feeder
My intent is to get pics of the birds inflight as they are either coming in or leaving the feeder. How do you know what to set the focus at ?
I don't want the feeder in the pic.
If I go to manual focus what do I set my focus to ?
If I use the feeder to set my focus and then swing the camera to the left those pics are out of focus because the distance is not the same
Today I focused on the feeder and shot as the birds were coming to it
The feeder is in focus but the birds are not
My plan was to crop the feeder out
Hope this makes sense
Thanks

Here is my take on the subject. If you let the birds free fly into the feeder, you are going to run into issues. You can maybe see if they come in a specific direction regularly and set up on that path. Then do a physical measurement to that distance and set your focus to that distance. You will also be better served to set up a aperture that will get a large depth of field.
The only issue you will likely run into is timing. I know that Magic Lantern has a motion sensing timer option and might let you get some shots. But I have found trying to time birds going to or leaving a feeder is almost worthless.
I have one of my feeders in the tree allowing for only two points of entry and I can occasionally get a shot, but more often than not, just taking the photo on the feeder has gotten me better results since they stay there for a few seconds at least.

Setup the feeder on the same plane as what the birds are staging from to fly to the feeder, Doing so allows your focus to be clear from the perch extension point as well as the feeder landing point.

The feeder needs to be small and narrow on the plane of the staging branch.
The staging branch can be a stick extending from a bush, another perch setup, anything the birds can extend off of before flying to the feeder.

The key is extension. a thick shrub or tree the birds will work there way out to the edge before flying to the feeder.

It's also key that the feeder is narrow, rather long to control the flight pattern of the birds. This method requires anticipation on your part. then shuttering away when the birds actively move.

Keeper rate is VERY low, but this will allow you to capture some shots.

another perception to consider: most focus on the feeder and maybe twigs they have protruding from it which birds may land on or depart from. But expand your perception of where are your favourable birds coming 'in' from and where do they perch before going towards the feeder? Are there preferred branches of trees? How are the 'Light' conditions on those branches versus the conditions before and after they land on those branches?

Maybe its not about the feeder but where they are coming in from.

What are your favourite birds favourite seeds?

As has been said, try to position your camera in the typical plane of focus of your fave birds coming in. Take lots of shots and continually observe their behaviours so you eventually predict their actions with your camera.