Rules for Generic Model Mirror/Copy Functionality

[BigPicture045]

I use generic models often for trim so that when used in groups they copy and mirror accurately. I use copy/mirror as a primary workflow as I am sure other do also. However, I am still running into instances where generic models are not copy/mirroring like their original couterpart. 

Here is an example of a around-window trim family that is a work-plane based generic model. You can see on the left it surrounds the window as intended, however, when copied to the right, the trim is higher:

Family Settings:

[syman2000]

I am trying to replicated your issue and can't seem to get the family to behave what you've shown. I just group the face base trim and did mirror. Do you have other item added to the group or this is just face base trim?

[BigPicture045]

I've attached the group. It includes a custom generic model window as well. 

[syman2000]

I look at it. It seems the frame is set to workplane base. The funny thing is this will flip the frame upside down. To overcome this issue, I would simply check off the workplane base and always vertical. When you mirror, it will stay the same.

Typically if you want workplane base to work properly, I would placed the object flat in the plan. When you mirror, it will work.

[BigPicture045]

I'll try unticking the work-plane based option.