The visual area of poison pools does not increase with items like Drought Release or the Acid Flask node Splash Zone. This is probably the case for idols/affixes as well but haven’t tested that.
Damage wise (and nodes like Hydrochloric Acid) still apply however even outside of the visual area of Poison Pool.
Lingering Toxicity (+x second duration to Poison Pools) also doesn’t last longer visually, but does still receive the benefits.
Finally, if the stat tooltip can be trusted, Hydrochloric Acid lasts twice the duration of your Poison Pool. So after 4-7 seconds of Poison Pools (or after moving out of them), you still receive 4-7 seconds of Hydrochloric Acid bonusses despite not standing in them. Seems like it shouldnt work that way