You have a mismatch between the crank and spindle.

Though the tapers are the same, various brand spindles have different size starting points (the distance across the tip). So, changing the spindle to one that's smaller at the end, will mean that that end will be deeper ito the crank.

To answer your question, it's not a matter of force. Once a crank begins to tighten on the taper, it can only move about another millimeter or two. All the force in the world won't move it deeper, though if you try hard enough, you can split the crank apart.