I guess my comment with regards to the temperature is more down to myself...even when its mid winter in the Flinders, or in Central Australia (I've walked there in July too) and its pretty cold in the mornings (maybe 5-15 Celcius) once I get walking with a pack, I start getting warm pretty quick-certainly enough for plenty of perspiration. Mind you, I sometimes walk with a much older guy (about 60) and he will still have a couple of thermals and a beanie on.
Rather than just "mozzie" netting mesh (I would say would defn irritate), there are much softer fabric meshes out there, that no doubt weigh a bit more, but are soft on the skin and still probably quite durable. Its a while since I've been to a fabric store, but I have (yes bad me) some "fashionable" pants and shirts that have this kind of mesh as pocket liners...Like the Columbia GRT pocket (on the right), and the pockets on my berghaus pants...the Berg Pants are where I got the idea from-I found leaving the cargo pocket zip open provided quite a deal of ventilation, while travelling.
Its not so much about your chest being the hottest part of you or not...it adds no extra weight (like pit zips) but could provide extra ventilation (that will help elsewhere by cooling blood down) when required for no weight gain.
I'll wait for your pattern. It will save me modifying one.