From side control I take americanas all day. Herzog has a painfully simple way to hit americanas. Even though I prefer the fun stuff, the Americana is still my highest percentage move.
From mount, I put my elbow to their elbow and drop my weight to wedge my elbow between their arm and their body. Once I get that space I snake my arm under until my bicep is going toward their armpit. Then you fingertip crawl to get their arm up by their head. Head/arm control. Arm triangle or sit up to s mount and do what you want.