There’s a few factors…amounts of certain snow crystals in the pack (feathery dendrites vs more compact crystals), strength of wind (drifting), relative humidity (sublimation), weight of snow in the pack (the weight of the snow upon itself), etc. I’m going to assume he had more water equivalent than you which explains his higher total. So the rates of compaction will probably be similar assuming you both had similar percentages of large dendritic growth. However he’ll still have more in the very near term… at least until those 30s creep in.