My H356 has the same foresail behaviour... very slack and sloppy. I have measured the mast rake as per Seldens tuning N°1. My local rigger has verified this too and says it's quite 'normal'. Unfortunately there are no methods to tighten the forestay without changing or shortening it
So after 1 year of owning and intensive sailing my H356 I haven't found a sail setup with the main to counteract the baggy forestay. Lots of tension on the kevlar halyard is about the best result. The same for the main halyard and main haul out both in Kevlar give best results.
Greetings from Marseille France.