AE lock on T6s

I have investigated the manual and the internet at length, and I cannot find an answer to this problem.

For the last 8 years I have used a Rebel that was very straightforward. I used P mode exclusively (unless I really wanted to control aperture) and made liberal use of exposure compensation. I recently upgraded to a T6s.

With my old Rebel, I got the exposure I wanted by simply metering an area using spot-metering and locking it with a  half-press of the release, and then re-composing and releasing the shutter. I was *not* using evaluative metering and I was *not* using AE lock.

With this new model, that does not work at all. When I press the button halfway and recompose, the camera seems intent to use the center point of the viewfinder as a new metering point, and not stay locked as I intended it to be. I do not wish to use evaluative metering because the point is to choose which part of the image I want to expose for, and then re-compose the shot. Hitting an AE lock button was not part of the equation before; I could shoot quickly without moving my finger from the shutter release.

I realize that in many ways I may not be the kind of photographer you admire and I am not seeking your commentary on that. What I am wondering is if any of you know if functionality has CHANGED over time in the Rebels that would cause this disconnect in my usage, or if you suspect something is amiss with my camera's metering function.

Thanks in advance.