Incorrect name I think
I only use normal Riccia Fluitans - the moss in the new layout is peacock moss.
I achieve small size in Riccia with frequent trimming and higher co2 concentrations and nutrient density. When I get these aquariums to fully grown in, I am typically running 3-4 times the initial recommended dosage for fertilizers.
This same technique can be used for E. Tennellus - which will grow quite large when left alone, trimming to the base Helps maintain a smaller size.
Often, the size of a plant isn't a new sp. of that plant, but small growing size is achieved with good trimming and dosing technique.
For example - E. Acicularis and E. Parvula will grow to about 8 inches left alone, but frequent trimming can train this plant to stay about 3-4 inches instead.
The same with stems - trimming them will keep lea sizes smaller and create denser foliage.
So the lesson here is that mastery and cultivation comes through proper care (trimming) technique, rather than specific species or sub species. The same practice comes into play with plant color.
In two tanks with the same dosing regime, one with frequent trimming (tank A) and the other with almost none( tank b), E. Tennelus is growing.
In tank A, Tenellus grows shorter and keeps a blood-red bronze coloration mixed with greens.
In tank B, tennellus over grows and becomes taller (about 12"), and the bronze coloration fades out to a light shade of green.
The trimming induces tennellus to regrow where it maintains it's beautiful bronze color before it "grows out of it."
In Rotala Colorata, as the thicket is repeatedly trimmed back, the stem size stays tinier as it is covering ground (e.g. It hasn't grown to full size yet). The tips maintain a gradien coloration between deep red at the top and yellow at the bottom. However as the leaf ages it turns more yellowish and eventually is green, so left alone only the top portion would be the brilliant autumnal color.
Think of the aquatic plants growth as a flower blooming - once it has bloomed it "peaks" and the plant grows beyond that stage. What we want to do is repeatedly maintain the plant in the most pleasant temporary state, which is achieved through trimming at the appropriate times. Overgrown plants are rarely a good thing aesthetically, unless you are specifically looking for the plant to be in it's "overgrown form."
So if we think of plants in terms of emmersed forms and submersed forms as the most obvious, then there are "sub forms" of the submersed forms (this is not technically, scientifically correct, but for understanding is easiest to visualize and think of).
Of those "sub forms" there are three stages - initial growth / re growth, where the plant part is spreading out a runner or a new plantlet or regrowing a stem. This form is usuall the smallest and has a slightly pale coloration.
The second and usually most "ideal" form is the maturing phase, where the plant has it's deepest / most brilliant coloration and the plant is of medium size (relative to max growth of that plant). This would be where tenellus is about 3-4 inches and has primarily bronze colors.
The third is overgrown or aged phase - where the plant has gone beyond full maturation and is now at or beyond maximum size - colors usually change again and are a little more faded or deeper in color depending on species. sometimes this coloration could be much different (like red to yellow to green in R. Colorata) or more subtle shades (like popping vibrant green to darker / subdued green in HC).
Another way to think of it is in terms of a human baby growing up and going through adolescence to teenage to adulthood to old age.
So in trimming we effectively restart the process again at initial growth and want to constantly be in the maturation phase.
This is also why it is important for you to learn a couple key species and to reuse them in your layouts so you can master their growth and phase patterns to make increasingly more complex layouts.