Bent knees remove the gastrocnemius from the equation (it crosses the knee joint and goes slack when the knee is bent), isolating the soleus. Both muscles need direct loading for complete calf development.
Soleus isolation — bent-knee position mechanically removes gastrocnemius contribution, forcing the soleus to handle the load alone.
Both heads required — the gastrocnemius and soleus have different fiber compositions and respond to different stimuli; both need direct work.
Same 2:1 lever ratio — same extreme loading requirements as standing. High reps with controlled eccentrics.
Placed last as the session closer, isolating the remaining calf head.