As I understand it…and I may not at all, it’s a backspin effect. The grass gets between the ball and clubhead, vastly lowering the coefficient of friction. The ball still rebounds off the clubface, but there isn’t as much torque applied to the outer surface of the ball. Backspin is greatly reduced.
OK, backspin’s gone, now what? Backspin provides, via the Magnus Effect, lift on a sphere like a golf ball. Drag comes along with lift. When there’s lift, there’s drag. Consequently, there isn’t as much lift on the ball holding it up from a pure ballistic trajectory, but there’s a lot less drag too. Velocity is going to remain higher, for longer, but ball flight will be more purely parabolic. The ball will run a lot more after impact too without a lot of backspin.
I expect the effect to be most pronounced where backspin is most prevalent, and that should be with short irons/wedges. Is that the case, everyone? That said, “greasing” the ball, applying Vaseline to the ball and/or driver face, to reduce friction and reduce spin, was supposed to be ‘one of those secrets’ Vegas guys used to get more distance and less offline drives. (No idea if Notah Begay’s infamous alleged spitting on the ball had the same effect)
I would ‘expect’ the flier effect to be where sufficient grass could get between the ball and face to kill friction, but not so much that firm solid contact with the center of the ball and the accelerating clubhead, couldn’t be achieved. Since you’ve stated you’ve been hitting downward more, and probably getting more compression on your strikes (though that’s not the only way to achieve that), you’ve been getting more spin. And really noticing now when the spin goes away.
Go to Trackman or Foresight’s online ‘Launch simulator’ and monkey around with spin values for a given clubhead speed and angle of attack, (EDIT: BZZZT!! It’s Flightscope’s. Here: https://flightscope.com/products/trajectory-optimizer/)
for a much better estimate of the effect than I could give you. My guess, from vaguely remembering Greg Norman’s golf book, where he discussed fliers, was that it was up to a 3-club effect. Though he did talk about a 300 yd 5-iron…so, yeah.
Me? I’d take one club less, for the carry, but I’d expect it to run. Judging by my ‘hit the ball’s equator’ shots—which also should really minimize backspin—jeez, another 30-40 yards of run for say a 7 iron?