Answer 1) The maximum height at which the solvent should condense (in the condenser) during the reflux should be halfway up to the condenser.
Explanation : If the solvent molecules exceeds the maximum height of the condenser there may be loss of molecules of the solution. The maximum height is maintained during the reflux so that the volatile molecules travels back to the solution and initiate the reaction process.
Answer 2) If the solvent condenses higher than this, then the solution vapors will go back to the reaction flask and start the reaction much earlier than before.
Explanation : If this is prevented by not allowing solvent vapors to exceed the maximum height of the reflux condenser then reaction will not happen fast or will not start early. Therefore, the condensation of the solution vapors should occur at the maximum height not higher than that.