Avoiding a wet, back side while hiking with a pack

The premise of the Osprey Airspeed suspension as featured in the Exos backpack line is that the mesh back panel suspended an inch from the pack will keep sweat from soaking our backs due to the air that can circulate.  My recent walks show a more complex picture.

In three days of walking I have a better idea of what to wear with the Osprey Exos backpack at air temperatures of ~35F degrees.  Never mind the last 1200 miles I walked on the PCT in 2015 with Osprey Atmos 65 AG, Osprey Exos 58 and some unknown REI backpacks, when the temperatures ranged from 40-70F.

Day 1. I walked 7 miles with a light load in my Osprey Exos 38, with its Air speed mesh back panel.  I wore two Icebreaker merino wool t shirts, a long sleeve pullover, fleece arm warmers  and a down jacket for a 33F degree day.  On completion, all the layers came off.  I had a wet front and back of the two t shirts.  The down jacket back was also quite damp and compressed.

Day 2.  I walked 7 miles.  I wore one wool t shirt, fleece arm warmers, my down jacket worn backwards and unzipped so that I only had one layer between me and the mesh back panel of the pack.  36F degrees this day and with a 6 mph wind.  The jacket came off when I had the wind behind me.  Once I turned back into the wind, the t shirt with fleece arm warmers wasn't warm enough.  I stopped on the leeward side of a building to adjust layers.  I continued walking with just the t shirt and the down jacket--it was too warm, I felt sweat on my arms and front trunk.  On completion, the back of my t shirt was slightly damp--unlike Day 1, I didn't have to hang the shirt on a line to dry.

Day 3.  I walked 3.4 miles.  Temp 35F with wind of about 9 mph.  I wore one wool t shirt, fleece arm warmers, a nylon shirt worn backwards and unbuttoned.  Again, only one layer between me and the mesh back panel of the pack.  Happily, only slight dampness on the back of my t shirt.  Nice.

The bottom line here:  To keep my the back of my clothing from wetting out from sweat, I need just minimal clothing to keep the mesh from irritating my skin.  Quite likely, in warmer weather, walking shirtless as I've done in 2015 will keep me dry.

Unrelated observation:  The wind rarely blew hard enough to require a layer on the back side of my pants. This raises the question of a clothing component system that starts with a front panel for a headwind and a back wind layer that snaps on when the wind does blow hard enough from behind or when we stop long enough to feel the chill from behind.