but can't quite see if there is positive evidence that the blockage/impingement is at the FOHE or if it's by logical analysis/plausability argument only. Could some patient soul enlighten me ? Thanks.
Ice blockage of the FOHE inlet has been demonstrated in lab testing. It was not expected and operational procedures have been introduced to alleviate it. RR has designed a new FOHE which is now subject of an AD.
There is a picture in this thread, and also in Flight Global.