Helper spring is only used to prevent the main spring from unseating at full droop. Length of helper springs needs to be long enough to keep the main springs seated when the suspension is at full droop.
Tender spring is used to help "push" the main spring down as the suspension starts to droop/extend (i.e., keeps the main spring "preloaded") as well as soften the effective spring rate if it is not fully compressed (two springs in series). Length and rate of tender springs are important.
I use helper springs on the front struts, and no helper or tender springs on the rear height adjusters.