Sweat rate variables

Since this is probably more of a long course issue, thought I would repost here vs the general tri thread where its getting crickets:

Hmmm...perplexed a bit here.  Have always been a big sweater, but it seems my sweat rates in training for my second IM are down vs those 2 years ago.  I am probably about 4 or 5 lbs lighter but % of loss to body weight is also lower.  I know temp and humidity make a big difference, but I dont seem to be losing as much on my long runs and was wondering what if any variables might alter this other than the obvious heat and temp.  Things that have changed:  body comp (water retention of fat vs muscle?), run fitness (better pace at same RPE), nutrition (using just gels and water vs gels/water/infinit in 07- have had questions wondering if infinit mix i was using was too much stuff and screwing up absorption).  Any ideas or am I just imagining that this has happened and sweat rate remains fixed?