What is a partial regulator?
I think, the graph you indicated, might saying the following matter:
Let's take an example. &quot; Some snails and fish  go into aestivation  to avoid summer-related problems-heat and dessication.&quot;  Now, when summer comes after the season Spring, the temperature gradually rises. The fishes can generally  withstand upto a threshold limit of temperature, and conforms upto this threshold limit. When their   comfortable weather breaks due to rising temperature, then they enter Aestivation and the graph now starts paralleling the X-axis.
Look, the graph doesn't parallel to the &quot; Conformers' line&quot; from the origin, but deviates with a little angle from that line : that implies the organism was trying to regulate against the external environment at first.
Undoubtedly, it's my own opinion, may carry some shortcomings generally.