Bicycle Mechanics - Splined crank/bb installation

I'm installing some RaceFace Prodigy splined cranks on my new ride and can't seem to get the crank arm to seat completely on the bottom bracket. I know it's critical that the crank arm mate flush with the stopper flange on the bottom bracket, but no matter how hard I tighten the bolt, there is still a 3-5 mm gap on both sides. I greased the splines and checked for burrs or anything else that could cause an improper fit and everything looks fine. I noticed that when I removed and re-installed the crank arm bolt, the crank arms seated a little closer. I've torqued the bolt pretty tight and don't want to over-tighten it in the process. Any ideas on how to get the proper fit?

You should use a torque wrench and torque the bolt to 350 - 390 lb in., that should do it.

Crank arms will only seat down so far as most bb spindles are tapered as to allow the amrs a point to stop on. This allows for clearnace on the frames chainstays.

If they are tapered like Shimano, they do not go all the way down.

When you were tightening them up did you get to a point where it felt like they just stopped, bottomed out. Then they are all the way on. The splined crank/BBs don't keep tightening up like the square spindles.