Answer: In commercial crops there are certainly recommended planting procedures based on not only seed type but also soil type and temperature and equipment and a host of other factors. In home gardening, seeds started outside will be planted deep enough to protect them from the soil surface drying out -- but the "rule of thumb" is in part based on seed size, in part on permeability of the seed coat, in part on season and length of germination time as well as other variables such as whether or not that particular seed needs more or less light to germinate. Seeds started inside can usually be planted much shallower than packages often suggest because the conditions are so closely controlled. For example, the two seeds you mentioned can be started (and if sprouting quality seed is used, eaten as "sprouts") using just a damp paper towel!
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