Seems there is a Bug in 7.8.2 & 7.8.3 that results in newer AMD Macs showing the wrong GPU Memory.
Update to 7.8.4 to solve the problem;
https://boinc.berkeley.edu/dev/forum_thread.php?id=11990#82890

Seems more than 10.13.x is affected,
Coprocessors : [2] AMD AMD Radeon HD - FirePro D700 Compute Engine (-2048MB) OpenCL: 1.2
Operating System : Darwin 16.7.0
Coprocessors : [2] AMD AMD Radeon HD - FirePro D300 Compute Engine (-2048MB) OpenCL: 1.2
Operating System : Darwin 16.7.0
Coprocessors : AMD AMD Radeon Pro 580 Compute Engine (0MB) OpenCL: 1.2
Operating System : Darwin 16.7.0
Coprocessors : AMD AMD Radeon HD Tahiti XT Prototype Compute Engine (-1024MB) OpenCL: 1.2
Operating System : Darwin 15.0.0
Coprocessors : [2] AMD AMD Radeon HD - FirePro D500 Compute Engine (-1024MB) OpenCL: 1.2
Operating System : Darwin 14.5.0
etc. etc...

I updated to see if it fixed my other problem...it didn't.

11-Nov-2017 08:51:05 [---] Starting BOINC client version 7.8.4 for x86_64-apple-darwin
11-Nov-2017 08:51:05 [---] log flags: file_xfer, sched_ops, task, sched_op_debug
11-Nov-2017 08:51:05 [---] Libraries: libcurl/7.50.2 OpenSSL/1.1.0 zlib/1.2.8 c-ares/1.11.0
11-Nov-2017 08:51:05 [---] Data directory: /Volumes/Mov1/BOINC/Yosemite/BOINC Data
11-Nov-2017 08:51:06 [---] NVIDIA GPU 1: GeForce GTX 1060 3GB cannot be used for CUDA or OpenCL computation with CUDA driver 6.5 or later
11-Nov-2017 08:51:06 [---] NVIDIA GPU 2: GeForce GTX 1050 Ti cannot be used for CUDA or OpenCL computation with CUDA driver 6.5 or later
11-Nov-2017 08:51:06 [---] CUDA: NVIDIA GPU 0: GeForce GTX 1060 3GB (driver version 9.0.222, CUDA version 9.0, compute capability 6.1, 3072MB, 2994MB available, 4082 GFLOPS peak)
11-Nov-2017 08:51:06 [---] CUDA: NVIDIA GPU 1: GeForce GTX 1050 Ti (driver version 9.0.222, CUDA version 9.0, compute capability 6.1, 4096MB, 3565MB available, 2255 GFLOPS peak)
11-Nov-2017 08:51:06 [---] CUDA: NVIDIA GPU 2: GeForce GTX 1050 (driver version 9.0.222, CUDA version 9.0, compute capability 6.1, 2048MB, 1992MB available, 1960 GFLOPS peak)
11-Nov-2017 08:51:06 [---] OpenCL: NVIDIA GPU 1: GeForce GTX 1060 3GB (driver version 10.18.5 378.05.05.25f03, device version OpenCL 1.2, 3072MB, 3072MB available, 1071 GFLOPS peak)
11-Nov-2017 08:51:06 [---] OpenCL: NVIDIA GPU 2: GeForce GTX 1050 (driver version 10.18.5 378.05.05.25f03, device version OpenCL 1.2, 2048MB, 1992MB available, 1960 GFLOPS peak)
11-Nov-2017 08:51:06 [---] OpenCL: NVIDIA GPU 2: GeForce GTX 1050 Ti (driver version 10.18.5 378.05.05.25f03, device version OpenCL 1.2, 4096MB, 4096MB available, 729 GFLOPS peak)
11-Nov-2017 08:51:06 [---] OpenCL CPU: Intel(R) Xeon(R) CPU E5472 @ 3.00GHz (OpenCL driver vendor: Apple, driver version 1.1, device version OpenCL 1.2)
11-Nov-2017 08:51:06 [SETI@home] Found app_info.xml; using anonymous platform
11-Nov-2017 08:51:06 [SETI@home Beta Test] Found app_info.xml; using anonymous platform
11-Nov-2017 08:51:06 [---] Version change (7.8.2 -> 7.8.4)

At least my problem doesn't appear to cause any other problems, other than being annoying.