I'll try and give you a history of the slate depth or shelf of the diamond table. Slate depth is very important to me. In fact this was an issue that got me in the pool table business. I played at a tournament in LA in the 80's. A funny thing happened. I found my cue ball froze on the rail half way between the side and corner pocket with an object ball deep in the corner pocket. I mean Deep. I couldn't even contact the object ball without first contacting a point on the far facing. This got me thinking about pool needs specifications to ever be considered a sport.
When I now talk about slate depth I'm talking about how much ball extends out into the playing area
while sighting down the rail with an object ball froze on the closest facing as deep as can be placed in the pocket ready to fall in..whew. Hope I haven't lost anyone. I checked the specification of a gold crown back then and found 40% of the ball to be visible. I followed thru today with that same 40%. Remember, gold crowns back then had larger pocket sizes of 4 7/8 to 5 1/8. Since my pocket size is 4 1/2 I had to have my slates made deeper to keep the 40% of the ball visible that brunswick used. Remember when you make a pocket smaller, as is being done on many gold crowns, you see the slate depth go away, which is not the way the gold crown were originally designed.