the fastest bow design possible built in the heaviest weight that can be pulled now fit that with the most skinniest string that would safely work,,,, now find the lightest arrows possible in the correct spine with the smallest fletch possible,,,,,, Now that should be a pretty flat shooting bow right there,, it might sound like a crossbow when shot but it will be pretty flat.
Now if its a bow I have owned, by far for me it was the Palmer Classic when I shot 2114 arrows, I won many trophys because I just had to point the bow @ 20yds a fool could shoot it......but I kept being told the skinnier walled aluminums would fail on big game so I bumped to 2016's then to heritage carbons ending up with 560gr heritage from a 50# bow not as flat as the 2114's that's for sure,, but that was the flattest I personally witnessed all due to the lighter arrows though.