If you use i1Profiler you can define a custom paper size up to 50x50 inches. No need to split the target into sections.
One question: why a 918 patch target? That was a target developed nearly 20 years ago by Bill Atkinson for ProfileMaker version 4 (perhaps even V3). You'll get superior results with an i1Profiler-created target. See
this post for more details. All else being equal, I recommend an i1Profiler target size that (a) maximises the number of near-neutral patches, (b) has a symmetric base color cube (i.e. the same number of RGB steps in each dimension, and (c) has an odd number of RGB steps from 0 to 255. We saw this combination to produce the best results within i1Profiler.
Sensible target sizes therefore are an 11x11x11, 13x13x13, or 15x15x15 base color cube with maximal neutrals. These give i1Profiler patch counts of 1457, 2371, and 3605 respectively. Either of the first two can go on a single 22" page layout from within i1Profiler.