Combustion (glyphed) and PoM share the same CD. 1,5min and Alter Time 3min.
So u can use Pom for every Combustion, not just the one with BL/TW.
Where u have to walk that much to use scorch?
If u time ur actions u can renew magebomb, use Pyroprocc or Infernoblast while walkin and in most cases u should blink anyway.
I've compared some of our logs (Elegon/Will normal kill, Feng Hc kill and Garajal Hc tries) And with my specc i am everywhere in front. And i did most of the fights with Ilvl 473 because i got bracers, ring and legs yesterday after raiding -.-
If u walk much Scorch maybe better, but is there need to walk that much? (exept maybe if u got chains with a meelee at stone guard). Just find good positions and try do do every movement via blink or if there are instants ready