Mehlin experimented with what has been called the Viola Plate. Rather than the soundboard being positioned parallel to the floor, it was inclined towards the keys.
The plate was inclined in the opposite direction. For this reason the distance from plate to soundboard increased approaching the tail end of the piano. And the bridges thus became taller and taller as seen in the pictures.
Other quirks of the Mehlins include a soft pedal that lifts the hammers closer to the strings as is done in an upright, small pedals, hinged pedal rods to eliminate binding as the back of the pedal arcs and sharps with rounded far ends like in some organ keyboards.