Unfortunately in the eyes of the law, the distance won't mean that fob can't visit, a solicitor or judge would be inclined to rule something like twice a month for 2-4 hours approx depending on age. Fob might also get away with paying less maintenance aswell if large travel costs are incurred in order for fob to have contact, although as it is him who moved away, not you, then CSA might not let him do that. In terms of contact once lo is older, if fob is still living more than 300 miles away, then he would get visitation for longer periods of time such as a week at xmas, several weeks during summer etc.
Obviously if he is unfit (smoking drugs) then you could have access restricted by being supervised and have court ordered random drugs testing.
There are other ways for contact to take place in a long distance situation like this, more for when lo is older but there is Skype, phone and letters if fob is too far away to visit often. xxx