MM8108-EKH19 USB Adapter doesn't compatible with MM6108 under EU 863-870MHz

Hi Team,

I tested the MM8108-EKH19 with Heltec H7608 and HT-HC33, it works wth 902-928MHz models, but when I test it with EU 863-870MHz model, I found it cannot find each other at all.

I see the main difference is that, MM8108-EKH19 support up to 2MHz with auto channel, and Heltec ones, only support 1MHz wth fixed channel.

So is this by design ? and we cannot mix MM8108 with MM6108 devices, for EU region, right ?