Reasonable values for the $\delta$ parameter:

delta

float[dimensionless scalar variable]

In renormalization theory based upon a non-interacting polymer, $\delta$ appears to approach a value of $2.5$. For interacting polymers, the matter is not so clear-cut, but one probably should not exceed $2.5$ by much since the exponent has the tendency to "damp out" the correlation. There is little meaning in a correlation of less than exponential square root as might be attributed to a spin-glass system or some forms of neural networks. Therefore, the value for $\delta$ has been set to the limits $0.5 \le \delta \le 3.0$.