The helix angle is generaly not considered in the calculus of tension springs. Anyway, if the initial helix angle can be negleted (coils are in contact, are at solid), the helix angle incearses with spring length.

The maximum helix angle is obtained at L2.

We consider that at this position (L2, F2), the helix angle should be lower than 7.5 degres in order to be sure that the formulae remain valid.