I am in a similar situation, meaning my pond has an excessive watershed and gets muddy from the larger rain events. So, I will be interested in the responses you get. I will add my thoughts with hopes of adding to your thread or at least getting corrected where I could be off base...
The closer to the pond the better, IMO. This leaves less ditch travel between the sediment pond and the fishery which should reduce the water picking up additional sediments. As long as the sediment pond overflow does not cause any erosion problems at the mouth of the fishery, I would think they could be back to back.
My concept of a sediment pond can be compared to a real wide and deep spot in a river. The water hits the wide/deep spot and slows way down allowing the dirt particles to settle out. So. the longer the water stays in the sediment pond the better the results. This leads me to think that the bigger the sediment pond..the better. With an excessive watershed, mine is about 5 to 10 times what it should be, I do not think I could build a big enough sediment pond...my 1/4 acre pond is likely smaller than what the sediment pond should be for my watershed making it a sediment pond all by itself. How big is your pond?
One might argue that if a sediment pond could establish a whirlpool effect that it could drop out more solids, but I will leave that to the fluid dynamic experts. Either way, it probably has marginal benefits compared to "inline". The key is to allow the water to slow down and have time to settle before moving on.
I do have a very small sediment pond right above my pond, kinda. It is what is left from a small old watering hole whose dam has washed out. It really does not allow any appreciable water to build up (12" or so), slow down, and drop out, but what it does do is collect logs which collect sticks which collect leaves which all act as a filter. Ultimately, the hole keeps a fair amount of "stuff" from making it to the main pond (it still lets the muddy water right on through). It dries up in between rains so mosquitoes are not an issue and the box turtles really love rooting through the mostly dry bottom muck in the late spring for bugs and such. Not really a sediment pond, but more of a natural filter.