RHP 2050
OTB 1885
Diff + 165.
I attribute this differnce to time pressure. My game is quite tactical so can be prone to mistakes when under time pressure (you are always under a certain amount of time pressure if there is only 75-90 minutes for a whole game). When I take time here I can analyse tactics in more depth and avoid the worst mistakes but when I rush here (as I often have) I can miss the most glaringly obvious tactics just like I do OTB and that is when I blow a "won" game.
I think that solid strategical players might find the difference somewhat less and it does depend on your style.