I'm thinking too that the lamb could well be put off by the mature tup over the fence. We've had this in the past, so we try to make sure there's no common fence between them, just a corner. With five tups it can be a bit of a shuffle.
This year we are using 3 mature tups and two tup lambs. One of the tup lambs I'm sure will perform well - he's been practicing a lot on his chums, so we've given him half a dozen ewes. The other seems very quiet and young, so we're trying him on a single ewe for three weeks, then we'll take him out and let a mature tup have a go.