Your sweet spot is the amount of product that produces the best hits/reactions for you. This post explains the process of finding it well How To Find Your Sweet Spot (How to find your sweet spot...) .
Instant Sexiness/B might work well on you, you never know til you try it. And it can actually work well on the shy, nerdy types on whom the IS/a might make you too intimidating, and thus the IS/b may make you more approachable to them.
MX300 is the ladies version of the men’s trust/confidence/respect product A314. It is primarily used in work situations, but can be used socially if softened with a social such as Instant Shine, Honesty or Openness.
And on using IS/a around people who already know you, it depends how often they are physically around you on a day to day basis. If you see them often, they may be used to your pheromonal signature, in which case it can take a few wearings around them for them to adjust and react to your new phero signature, so don’t be disappointed if you do not see reactions right away. I’ve personally had better luck using Instant Openness and Instant Honesty around people who know me for some reason. It also depends if they are family or not, because if they are, you won’t get much of a “sexy” reaction from them using Instant Sexiness.