Only the data type, length, data type and CCSID are inherited with LIKE. To pass an array, use both LIKE and DIM:
dmypgm pr extpgm('MYPGM')
d myarr like(myarr) dim(%elem(myarr))
d somevar like(somevar)
d myarr s 64a dim(100)
d somevar s 65a
See the 6.1 Infocenter LIKE() keyword.