Entirely agree with your last post.
If the FOHE has ice in the Fuel passages, care must be taken to avoid a sudden increase that disturbs the ice upstream, allowing it to drop and block completely the exit of the Fuel passage from the FOHE.
I thought the "possible problem" as identified by AAIB was an ice build-up on the inlet tubesheet of the FOHE. So the need would be to prevent ice release from upstream, not from within the FOHE. Once out of the tubes, the ice would immediately pass out of the FOHE.
If I read it right, the proposed RR interim fix addresses tube protrusion from the tubesheet, effectively making it smoother with less places for ice to catch and build up.
Sooty