Answer: Japanese maples tend to form a layered branching structure, and many are more of a shrub form really than a single trunked tree. Often they will branch low in order to shade their own roots and naturally work to keep the soil cooler and moister. This may be the form that the larger tree is trying to take.
They are amenable to pruning, and this is sometimes done to enhance their natural shape or form or to try to accommodate them to a specific location. So your plan is probably technically possible from that standpoint.
However, it is possible that the two trees will be in stiff competition for moisture and nutrients and one may overwhelm the other in time. This may be part of what you are seeing already.
Dappled shade or morning sun is generally the best the of location for these plants. The leaf scorch could be caused by excessively hot sun, so using the shade cloth might help although it will be relatively ugly and will probably need to be in place for the life of the tree.
Leaf problems can also be caused by other factors such as too much heat, lack of moisture/humidity or a nutrient/soil problem or even late spring frosts or excessive wind.
At first guess I would expect it to be heat possibly exacerbated by improper watering. The daily light sprinkling routine is undesirable for several reasons. For one, it encourages excessively shallow rooting making the plants even more prone to moisture stress. It is better to provide a good slow soaking less often and then water again when the soil begins to dry -- check it with your finger to know when to water again. A layer of organic mulch several inches thick is also important in helping to moderate the soil moisture and temperature.
You might want to run some basic soil tests to make sure the pH is acceptable and to determine just how much fertilization is required. These trees are not fast growers as one might be mislead to expect judging from other types of maples. In some ways this is a benefit because they are slow to outgrow their allotted location. On the other hand it means the results can be slow to appear in the landscape.
"Viridis" is often used as a catchall term, so which specific maple the smaller plant is, is anyone's guess beyond being a green-leafed dissected variety. If it was grafted, the nursery may be able to give you an idea of what to expect. If it is a seedling, there will be a certainamount of variation in the mature plants. Note that it is quite possible that this particular tree is more heat/moisture sensitive than the other. It is also possible that for some reason this tree has been slower to establish than the other, either due to competition or possibly to an overall relatively weaker constitution or even due to mishandling at some point in the growing/wholesale/retail/planting process having caused it to become rootbound or have some other root-based or graft-based problem. Sometimes, in other words,it is just beyond the gardener's control.
"Boskoop Glory" is the only named variety similar to "Boskop" I have been able to find described, and is said to be a red leafed form reaching approximately 15 feet in the landscape. Perhaps this is the one you have.
Keep in mind that a larger caliper tree will take several years (even three or four especially with naturally slower growing trees) to become established after planting, and will only reach its typical growth rate and vigor once it is established. Even so, I would not expect a Japanese maple with some age on it to grow faster than about six inches a year or so. A younger plant would of course grow faster.
In my experience, it would possibly be preferable to move the smaller tree to a different location and to use a shade tolerant shrub or possibly a piece of sculpture or other physical object to balance the larger tree in the composition. This way you will be able to grow both of the trees to their full potential.
I know that is probably not the answer you wanted to hear. You could also consult on site with a professionally trained, certified arborist to see if they have any suggestions as to what you might do to accomplish your original goal. Good luck with your trees.
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