Martin,
It's not critical to have a lot of distance between the ECU and receiver. In my Enforcer, which is a similar type plane, the ECU and receiver are about 4 inches apart. They are at the same fore/aft position on opposite sides of the inner fuse. It hasn't been a problem for 150 flights.

As much as possible route the wires to the ECU on one side of the fuse, and the wires to the receiver on the other side. There are a couple of places where mine cross.

The most important considerations are to keep the fuel pump away from the receiver and to route the antenna wire away from the ECU, pump and any other wires. I have my pump in the back near the engine and the antenna wire is routed out of the fuse and down the leading edge of the wing.

If you have a probem locating things were you want you can always make an extension harness for your ECU or use longer servo extensions.

Joe