Dutchmen Help

I'm making some Dutchmen(butterfly shaped) to reinforce a repaired chair seat. Also, I'm making my own patterns. I have a couple questions that some of you with experience with these critters can help me with. 1. What is the appropriate height to width ratio? 2. Is there a best angle to cut the sides. 3. Does rounding the corners and waist present any structural negatives? I have a feeling that cutting the waist portion at sharp angles may present a site for failure starting.
FWIW I bought a Chinese made, Shop Fox label inlay set at the KC ww show for $20. For practice I'm using some scrap pieces of oak. I cut the hole(cavity) 1/4" deep and the Dutchman from 3/8" stock. Trimmed the Dutchman close, beveled the bottom and pounded it in. Sanded it down flush and it really looks cool...
Lawrence L'Hote
Columbia, MO
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