Phil,
Welcome to HW.
Sounds exactly like me, and is a good sign as well.
Think of your bladder, gravity, and being prone. Holding at night, with your urethra on the side because of the prone position, means that you have a minimum of control (as opposed to none, which happens to some guys). During the day, gravity is working against you, as the urethra is now at the bottom.
Good news is you have some control. Bad news is you'll have to work a bit to get the rest.
My uro suggested Kegels, and my "magic number" was a set of ten done three or four times over the day. It took me five months to move from a Depends pant and eight+ pads a day down to one pad a day.