Nandrolone Phenylpropionate has a Molecular Weight(MW) of: 406.5638
Nandrolone Decanoate has a Molecular Weight(MW) of: 428.6538
As a point of reference Nandrolone has a Molecular Weight(MW) of: 274.4022
So not a whole lot of difference in length of ester there, although phenyl is obviously somewhat shorter.