CydKnight
Explorer
What do you do when life inevitably occurs and you have a player miss a session while the rest of the party is present? Does the player still level up at milestone like the rest? This could create feelings of unfairness for those that do attend every session. Maybe you don't have players miss sessions or do not hold the session if all players can't be present?What a curious game. The only way to win is not to play.
The best approach is to award a level at milestones and not waste time calculating XP for advancing, but instead use it only as a limited guide during encounter creation.
I give a level at each milestone. A milestone occurs roughly once every three sessions (although levels 1 and 2 are faster and the highest levels stretch longer. A milestone occurs in a natural break from adventuring (completion of a dungeon, etc...)
I've used this system in 5 different decades. It has never failed me and I've never second guessed it. Calculating xp per creature as a reward is a waste of time and provides no real benefit that a generalization can't afford.
I can appreciate and even envy that it has worked for you for 5 decades but I don't see it working at mine. At one time or another everyone in the party has missed at least one session over the past year but some have missed more than others. I cannot justify to the players why everyone would level up at milestones when some may have missed multiple sessions during that part of the campaign while others didn't miss any.