cannot transfer facetime from ipad mini 6 to macbook

I have an iphone mini 13, an ipad mini (6th) gen and a macbook. Using Facetime , I can transfer calls back and forth to the iphone and mac seamlessly. I can also do this with the ipad mini and the phone. However if I receive a face time call and I answer it on my ipad or I am on a call with my ipad I cannot transfer it to the mac. THe scenario is that I often leave my macbook on in my office and have my ipad mini with me. When I call comes in on the ipad mini there appears to be no way to transfer the call to the mac - nothing shows on the mac to allow this to happen. If I take the call on the iphone there in no issue. All three device are using the update OS's. Is this a bug or a design limitation