Hi Francois,
We currently do not have a sizing guide for an ICON that is specific to LRM. That being said, since an ICON with just role=LRM does not collect voice or user data, it will be significatly less than a voice ICON. It also would not collect any cfg role information. So, you will need to use some discretion, but the ICON sizing guide minus any voice and user-data should give an estimate to start with.
Best Regards,
Neil