I've found acroyoga or other variants of partner acrobatics amongst the easiest activities to get into a flow state. I think it's because there is lot of novelty, a high-perception of risk (although is actually quite safe), and a high requirement for coordination. I would describe it as literally forcing you into the moment. Whereas when I run, practice yoga, lift weights etc., my mind is elsewhere.

I would agree. It is harder to get into "flow" mind-state when traditional or aid climbing. You need to stop to think when placing protection unless it's a very straightforward placement. In general, the more you run it out, the more time you can spend in "flow", although obviously there are potentially high consequences, and your mind will be screaming at you if you are, say, dangerously run out above a ledge, or if you placed protection absent-mindedly and now you are second-guessing how much you trust it. Free soloing is the extreme end of that: maximum flow potential, maximum consequences. Top roping is probably the best bang-for-your-buck in this regard: maximum flow potential, minimum consequences.