Custom shims for engine mounts

I noted that for all four engine mount points, secured by M5 bolts, a small gap is visible between the engine mount surface and the upper and lower firewall mount channel. Tightening the M5 bolt I suppose to close this gap by flexing the channels along their centre line. I am not so keen on this unneeded introduction of stress risers into the channel. Instead I fabricated shims from 0.4mm 6061-T6 to fill such a gap.