lower shrouds angle

[benz]

I'm in the throes of designing a gaff rig for my Cape George 31' , and was advised by a master rigger to attach the lower shrouds higher up the mast than what I had drawn, so that the gaff should have more room to swing. Moving them higher, however, decreases their angle from the mast centerline to less than the 12 degrees suggested as a minimum by the "Rigger's Apprentice". It has occurred to me to bolt a plank to the hull where the chainplates are to go and bend them around the outside of that, to give more width down there, but this doesn't seem to widen the angle all that much, at least on paper.
Any suggestions?