There's a potential tick of searing totem, a precasted LB, and a potential LvB proc; plus everything else that's in yours other than the potential for ONE extra LvB proc that would further delay ascendance, possibly causing you to lose uptime from Skullbanner and other raid CDs. Not only that, you are running EB, meaning you have an extra ~2secs for that LvB proc that I wouldn't have due to running PE; which likely means that I am already sitting at the maximum possible LvBs prior to ascendance that PE can accomplish. I'll take my chances.
I already stated in a previous post that if you run with PE it is different, but the OP isn't..which is what we were discussing in the first place...I'm going on about topping dps with OP's abilities...not yours. :P Delaying Ascendance with 1-2 GCD doesn't matter...it's 500k free dmg.
Also, there's no way in hell you're seeing 80% chance for two procs in the space of... what... 5 seconds? You would need something like an 82% proc chance from ticks for that to be the case. As far as I know, Lava Surge is a 20% chance. Meaning the chance of getting 2 procs in the space of 5 seconds is somewhere around 20% ish, assuming 3 ticks of FlS.
Try it before you say it isn't possible, it is possible, and happens really really often.