It prolly will not look as attractive at the least I say put two plates adjacent to the neck. I did this and yes at 240 pounds plus a heavy bike I felt a lot better after this.
The strength of just one fish plate is over rated I think. It will not hurt to look in this forum for a while if'n ya don't mind reading.
Frame Building - Mountain Bike Forums
I believe the term they use is called smoke out out for bad fish plate bracing.
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