Oca tubers form close to the roots of the plant, but also where stems come in contact with the soil - up to several feet away from the original planting location. Seeing this mass of small tubers today reminded me that last year, although the total yield (weight) was fine, a high proportion of the tubers were too small to be worth cleaning and cooking.
So how to maximise the proportion of large tubers?
Remove some exposed tubers while small, so that the plant's reserves are concentrated into those remaining?
Prevent stem-rooting (by keeping stems from contacting the soil) so that only the tubers associated with the original roots form, giving fewer, larger, less dispersed tubers ?
Either of these approaches would detract from one of the crop's great plus-points - it is zero-work. Others have grown Oca in containers, which might limit the stem rooting tubers, but I have not heard reports of larger tubers from this method.
I'll let the crop run it's course this year, but this is something to ponder, and maybe test out next year.
UPDATE. An example of training Oca to grow upright (using canes) here: Thriftyliving