Thank you for the insight and kind comments. Certainly, some of the plants in question are shaded by floaters. In fact, I had to do a sizable trim last night just to take some of the pictures below.
The point made by talontsiawd certainly has some validity, imho. Looking at my 2 nanaos through other's eyes, I have other guesses as well:
The depth of the substrate in nanos is commonly shallower then in 'full size' tanks. Frequently I plant with rhizomes hitting the bottom of the tank. So, the small size of the plants might also be partially attributed to restricted root growth.
The follow-up observation is that some of my 'nano' plants are packed very tightly together (as observed by others in this thread), witch further restricts the space available for roots. The plants also might feel 'suffocated' by surrounding plants.
My partial goal for this thread was to try to determine specific set of conditions that would keep normally large plants nano-sized in smal aquaria, i.e aquatic version of the art of bonsai. Assuming relative equality of light and nutrients across differently sized tanks, the root development (like in bonsai) could have direct effect on plant's size. One way to test this theory would be to plant a large sword in a large tank completely in the open and to embark on a methodical regiment of cutting the roots. Comments?
Now for the pictures. All plants have been in the same location for ~9 months.
Sword, Lotus, and Hygro before HG trim:
Same plants after HG trim:
And now for some fun: I took red tiger lotus as my subject. All of them came at the same time from the same mother plant and were replanted within a day from each other in 4 different tanks:
Tiger Lotus in 65G under 6 x 54W of T5HO ~26" off substrate. The plant spans the whole depth of the tank at 18", reaches the surface at 18" and is about 18" wide:
Tiger lotus in 75G Tall under 4 x 65w CF ~26" off substrate. Much skinier then the previous one, about 20" tall, 8" wide (the light bulbs are old and the plant is heavily shaded):
Tiger Lotus in Finnex 4G under Finnex 26W 14: off substrate. The plant is < 1" tall, about 2" in diameter, planted 95% in the open:
Tiger Lotus in Mr. Aqua 12G 36"-long under 2 x 39w T5HO 9" off substrate. The plant is ~0.5" tall, ~1" in diameter, heavily surrounded by other plants: