The ground location will not be an issue. You can place the grounding block anywhere along the (max 200' for DP or DDP. max 100' Legacy) run. If you have copper water piping the tech would be able to ground to that as well. We are also allowed to ground to the AC compressor service disconnect (at least my company tells us we can). The 20' rule applies to the distance from the ground block to the ground source itself.