Which seems to be more effective at helping a girl open up around me? IO or IH? Which have you guys had more sucess with?
For closeness and depth of conversation - IH, by far.
If this is someone you already have met and will be talking with one on one, or in a small quite group, I’d say IH.
But there is no way of knowing for sure except to try them out. It seems to me that people either have a very obvious reaction to betanol or none at all.
You can also combo them to get little variations. A little bit of IO combo’d with a little more of IH gives the person a willingness to keep the deep conversation going. Reverse that and it gives the person to keep the conversation going, but with a little deepness to keep it balanced.
The idea is to experiment to get variations that suit different scenarios 
IO is quantity.
IH is quality.
For ‘opening up’ and being silly - IO.
For really opening up as in personally, secrets, desires etc - IH.
If you’ve got both - use both!