I build boards with vacuum infusion and use 30gsm c- glass fleece to improve resin flow when needed(e.g for carbon titanal laminates). But for hand lay-up I'd think you are better off properly wetting the carbon and pre- wetting the core. The glass will not necessarily make it stronger. For your lay...

I have done several boards where I put in the sidewalls seperately. I let a biax layer from the top laminate run down behind the sidewall for increased torsional stiffness. Worked fine. However, it is more hassle cause you need top profile the sidewalls separately. This was for vacuum and later vacu...

Bit late reply maybe...

Anyway, it seems to me that the transition from the mold base to the mould nose section is not smooth enough. If there is a bit of a kink, the core cannot follow the curvature and there will be no pressure below the core.