Have been wondering for quite some time now, about these huge discrepancies regarding when boards gets "too" small....
I think it is all about area (width) and volume, besides length.
Looking at the boards from Oldman_Dave they seem very wide and round edges so some thickness also?
Yours grigorib - difficult to see their thickness?
Mine are between 15 and 20 mm thick, and not too wide (will catch in chop and waves if wider), but the supershort pocketboards you have shown in photos looks like they pack some both area and volume?
If you ride in flat water or really small chop water, it is fine no need for more length.
But I have a hard time seeing how these short boards handle whitewater when not on foil?
I know when I make floater off the lips, I crash quite often, as the lift from the wing gets sucked out of the foil so you drop to the whitewater frenzy, and here having a nose on the board which is pointed up, makes a h... of a difference IMO.
Like last weekend - sometimes it works, other times you get tumbled, like this shot from last weekend:
It seems like it went okay on this picture, but a splitsecond later the wing got sucked down from the tumbling whitewater, and only chance to ride it out is to have some nose on the board, and some area too - so you can ride on the curling whitewater.
As said, sometimes possible to ride it out this way, and at other times you (I) get munched by the whitewater as it has a tight grip in your wing and mast and try to tilt you, so a lot more difficult than if it was a surfboard on the curl
Kite is partly drifting so nothing to support you...
Would be quite easy with straps yes, but without, not easy but fun to see how far you can go
In short: Some ride in flat water, where length is not as needed.
And when in flat water, but low winds or low powered, some short boards carry a lot of volume (thickness and width), thus corresponds to a longer board somewhat, just more compact (nice).
Finally, some ride with more power in their kites, or use kites with lots of peak powerspike - thus you can get up on foil immediately quite often, and here length/area is not important.
I think this is some of the reasons why we have so different views on this, apart from individual liking of course.
Peter