1. Test the shape before anything else
Get into the geometry before any penetration: one partner lies on their side, the other lies across at a right angle, legs resting over the sideways partner's hips.
Stay there for a moment and ask one simple question — can we hold this shape without strain? If legs won't rest, hips won't line up, or you slide apart the moment anyone moves, that is useful information: this position may not fit your body combination.
Unwrapping into plain side-lying is a normal outcome, not a failure you need to fix.