[bucketfoot]

For starters there is pretty much only one optimal configuration for any shared platform, with all others have various compromises.

A second is the designed usage. Take something like the Camry platform. A Camry is naturally going to have higher reliability than something like a heavier, taller, etc vehicle such as the Highlander. Also in cases like this there are some variants such as AWD. This alone decreases the reliability.

Next, vehicles of different price ranges can be built on the same platforms. The lower end models will generally have cheaper parts used in some areas of the vehcle.

For engines, like a platform there is one ideal usage. Using the same engine in say a passenger car and an SUV can result in very different levels of reliability. Additionally there can be variants of the same engine. Take BMW for example where there are different versions of the B58. In general a higher HP version is inherently going to have lower reliability than a lower HP version.

And then yes, where a car is made and where the components are made also can play a large role.