The spring barrel (Y, S, straight) has not bearing on fitment. This typically affects the progressive/linear behavior of the spring. Btw, you are only measuring I.D. on the top and bottom most coils only, correct?
In this particular case I was eyeballing the size of the seat on the underside of the mount, and the ID of the spring, but yes, referring to ID.
I’d say the diameter of that top coil manifestly has a bearing on fitment. It has to have an end coil which gets to a small enough size to mate with the mount.
That said, if the top coil is too wide to fit the Mazda 5 top mount, I'd think the solution could be as simple as getting matching CX7 top mounts. Look at some parts diagram to get a quick visual confirmation. The top mount consists of bearings+isolator fitted inside of a hard mount housings. This part 'should' be interchangeable b/c the top mount only uses the shock piston nut to secure the spring; the top housing mounts the whole assembly to the chassis. What needs to be confirmed is if the Cx7 top mounts aligns with the 3 holes on the Mazda 5 chassis, which I'm betting it will.
Not a bad point. I just looked it up and the CX7 uses a four stud connection vs. the three bolts on the 5. Even if you could somehow mount the 5’s top plate onto the CX7’s bearing assembly the 5 uses bolts which thread into the top plate vs. studs which go up. So they’d stick right through the plate and into the top of the spring. I’m just calling it on the front springs.