Besides direct damage to follicles, miniaturizing hairs can be negatively affected by the general trauma of surgery on your scalp. So even if the doctor is super careful, surgery can still cause shock loss. What might be somewhat helpful: If the surgery is not in the immediate area where miniaturization is occurring (for example, grafting into a bald frontal area, while being concerned about miniaturization in the crown.) And perhaps not doing a very large number of grafts (a smaller surgery might be less traumatic).
Researchers might not want hair transplant patients for test subjects, because hair transplant cause scarring in the scalp. A hair transplant graft is a skin graft (which just so happens to contain a hair follicle). The scars in the recipient area may be small (and camouflaged by the hair follicle) but when you have placed hundreds (or thousands) of grafts, that scarring may be considered a disqualifier to researchers. It may be considered to affect circulation. It would also look very suspicious in Before/After pictures ("this patient obviously had a hair transplant! Test results are probably fake!")