I'm starting my third month on a recumbent (AB HiRacer), using it daily for commuting and for other occassions. I recently found out, and am currently experimenting with, a technique to take sharp turns as well as going over bumps such as found in grass, dirt paths, etc... It consists to sit more upright. I guess this concerns 'European recumbents' (eg. Challenge, Optima, etc... in which the rider is more laying down than sitting squarely). If it's then possible to pedal and steer while being upright then it's possible, I found, to achieve much more steep turns like closed angle turns (providing the heel of the shoe is tossed on the side). It also helps going over bumps on suspensionless bikes as there's less of an incentive for the front wheel to jump, control is more easy to keep, and the bumps simply are not bumping in the back.
So I'll be adding this technique more and more as opportunities to do so happens. I guess there's nothing new with this, as I've seen it on some videos from France (Optima bikes on downhill singletracks with roots) and surely it is well-known. It's a nice technique to have.
I'll scooch back in the seat a bit if the going gets very dicey: typically only on extreme trails (like 20+ degree descents with lots of gravel), icy patches, washed-out bridge underpasses, or if rush-hour traffic is making me nervous at a stop light. I never leave the seat, though -- well, not intentionally!
For really tight turns such as those that reach the limit of my indirect steering (Challenge Seiran), staying relaxed works better for me.
I will raise my head off the headrest to move my helmet mirror around when merging left, to avoid getting smacked in the back of the head when going over extreme bumps, and to help me look through tight turns or to look for vehicles when approaching intersections.
For REALLY tight turns at high speed, it seems that your tires are most important. Less volcanization (software rubber), less air pressure (for a wider contact patch), and wider tires would enable tighter turns with better safety.
Come to think of it, perhaps there's a psychological aspect to it. Or perhaps not. Perhaps it has to do with physics. Or both. But while sitting up I found it is easier to steer in tight contexts and I'm not sure it has to do solely with physics. The weight is put a bit forward and on the Ab HiRacer this means closer on top of the front wheel along with the steering activity right there. The easiness comes from there. But then I appreciate that it is possible to also lay way back for normal rides. I wouldn't like to ride all the time like this.