DECT cordless phone with Telecoil (T switch) aid setting

The web page https://www.actiononhearingloss.org.uk/shop/phones/cordless-home-phones/  states:

"To help make calls easy to hear and understand, most cordless phones for people who are deaf are hearing aid-compatible. This means you don't have to remove your device when using the phone, you can listen through your hearing aids on the hearing loop setting. "

I believe most cordless phones in 2018 are DECT.  I have a BT4600 DECT Cordless phone which is sold as "hearing aid compatible" and is explicitly stated to have an "inductive coupler" in the handset.  I have tried its handsets both with my new Widex Evoke Fusion and my older Phonax Nathos S+ M aids on T setting and only get nasty buzzing.  Both phones work very clearly on T setting in buildings with a loop.

It may be that the BT 4600 is faulty, but I wonder whether it is the DECT signals that are swamping the loop audio.

Does anyone have experience, good or bad, of comparable situations?