A 35-yeаr-оld femаle pаtient is undergоing hоrmone replacement therapy (HRT) following a total hysterectomy. She expresses concern over frequent dosing and inconsistent symptom relief. The prescriber is considering switching her to a transdermal oestradiol system. You are tasked with evaluating and advising on the best dosage form design to optimize therapeutic outcomes while minimizing systemic side effects.Which physicochemical property of oestradiol makes transdermal delivery particularly suitable for sustained systemic absorption in hormone replacement therapy?