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Yea I use R/S as much as possible for RNGing random wild Hoenn captures (Trapinch, Bagon etc). Easier to RNG ID, easier to hit a frame because you can change the time on an emulator and so on. And Sweet Scent works fine in R/S, do you mean Synchronise?
Seed generation in FR/LG is determined by taking a value from a clock that is running at 16 MHz which is a few hundred thousand values per frame. So basically what I did was start the game, make sure I press A at exactly 300 frames, and then again at 700 frames (you need to press A twice minimum to get to the point where the seed generates). You won't always hit the same seed, but you will start to hit a few seeds on a regular basis, so you should note these down. If they are all bad, just change a value, for example press A at 701 frames instead of 700 and see what you can do.