What is the maximum height at which the solvent should condense (in the condenser) during reflux? what might happen if the solvent condenses higher than this?

The answer to the first part of question is: During condensation in reflux condenser, the maximum height is halfway up to the condenser.
And the answer to second question is this that if solvent condenses higher than this maximum height, all of the solvent may run back into the reaction flask or may be the reaction will start earlier. if the solvent do not go up than the maximum height, the reaction does not happen to start earlier.