I'm guessing by looking at your earlier posts that you are building the "Sea witch"?
I've seen two sail plans for "Sea witch", one in "The search for speed under sail" by Howard Chapelle where it looks like the forestays go to the bowsprit
http://www.histarmar.com.ar/Clippers/Fotos/021%2028a%2015%2015%20x%209.jpg
and a book "Ship models - how to build them" by Charles Davis where it looks like they go to the knightsheads.
http://www.pietrocristini.com/clipper_sea_witch.htm
Looking at other sources, e.g. "The American-built cipper ship" by William L. Crothers -
"Fore and mainstays went double, generally to a seizing not far removed from the point where they were to be set up. For the forestay, this end was generally the knightheads..."
The brig "Irene" by Petrejus also has her forestays at the knightheads, as does Andrew Bowcock's raider C.S.S "Alabama" and the clipper "Thermopylae"for example.
?action=view¤t=thermdeckbow.jpg
However, H.M.S. "Victory" has her forestays seized to the bowsprit, as does U.S.S. "Constitution", the frigate H.M.S."Diana", many of the bluff-bowed merchantmen and some with clipper bows in Chapelle's "Search for speed under sail".
My guess is that it has to do with the shape of the hull, the distance of the foremast from the bow and the height of the foremast. I guess the angle of the stays would have to be within certain limits to be effective. If the bow was bluff, the foremast would be nearer to the bow (e.g. HMS Victory), so the forestays were seized to the bowsprit and the bowsprit reinforced with gammoning, bobstays etc. If the bow had finer lines like a clipper (e.g. clipper "Challenge") the bow would extend further forward of the foremast to help preserve buoyancy and the forestays could be seized to the knightheads if the angle was within the limits. But that's a guess..