Gaps between zones doesn't make sense as they are concurrent so you are always in a zone. There are 5 zones and the default seems sensible to me. Why do you want to change them? If you really do want them customised then create a zone 3 between your 2 zones and call your zone3 zone4.
HTH
CW
Zones have to be contiguous. Simple. The idea's nice, but the practically is not.
When training, ensure you don't ride the fence :)