Taking your TARGETC region as example, you are now using the body targetC to build the region. However, better practice would be to use a ZCC and two XYP. The ZCC would have the same radius as your targetC and the two planes (targetP1 at z = -38cm and targetP2 at z = -2cm) should be located at the z positions which are the start and the end of the region. To build now the region, you proceed as per usual, selecting all the bodies that make up the zone: +targetC +targetP2 -targetP1. If you add a plane, as it is the case here with +targetP2, FLUKA is considering the portion of space with lower values of the z coordinate (i.e. on the left of the plane), while when subtracting the plane the space portion with higher z-values is considered.

Now, you also can use these planes in the neighbouring regions like SPACER1 and SPACER2. The infinite cylinder you should use for all components with the radius of 1cm. Proceeding like this, will reduce the amount of bodies in your geometry and, more importantly, reduce the likelihood of errors in the geometry.

Please have a look as well into the slides of the last FLUKA course, where the use of planes and other bodies is explained in greater detail.