Warm Tank

Hello all I did a decat x pipe on my speed twin and thank god its finished, I only had 50 miles worth of fuel in the tank I did run in for a while switch it off for 50 mins then went for a quick run throttle response seems better sound is beautiful but I noticed both side where my knees rested was much warmer than normal? I never noticed before I decatted any warmth from the tank is it because the tank is low on fuel it gets hotter or could there be another reason or am I worrying over nothing ,it just seems strange.

 

Thanks I thought it could be low level causes heat to build up over a smaller volume of liquid, has anyone on the site done a before and after dyno run on a thurxton, speed twin to see if indeed the xpipe does increase the power,torgue curve I'd love to see a chart