Difference between test propionate and phenylpropionate?

Can someone please tell me the difference between the 2 esters and how it is is possible for PGW to put 40mg propionate plus 40mg phenylpropionate along with 100mg enanthate and 100mg cypionate into 1ml supertest but only a maximum of 100mg prop in 1ml for the prop alone version? Thanx

The ester lasts about 2 days more that prop, but is still advised to inject every 3rd day.