The best way to check a digital humidity sensor is with a Sling Psychrometer. There a a few on Amazon, this one is $62: https://www.amazon.com/Forestry-Suppliers-Non-Mercury-Pocket-Psychrometer/dp/B01M1PFCKL/ref=sr_1_5?crid=1JB59FVENJD0Y&keywords=sling+psychrometer&qid=1674825317&sprefix=sling+psy%2Caps%2C83&sr=8-5

would I drop the rain offset by 8% so instead of 1.0 it would be .92 ?

Also ... what does it mean by a range of up to 6000mm?  It breaks after 236" of rain? 

Yes, to reduce your actual gain by 8% multiply it by 0.92 ( in your case, i think 1 * 0.92 = 0.92 )
The 6000mm limit derives from the 16bit count value the sensor transmits ( 65535 *0.1mm = 6553.5mm )... but when the count nears 59999 you better watch out of strange fellows loitering around your sensor... 

Weather Display also supports the Ecowitt Gateway API (used by GW1000, GW1100, GW2000, WN19x0, WH26500 consoles).
It only needs to run inside the same local network where your console (GW1100) is connected to.
To which router/access point you connect your GW1100 is immaterial (as long as it is inside the same local network as WD). You just have to make sure that the gateway receives your sensor (array) data and is connected to the local network.
If the GW1100 receives teh sensor signal also in your garage, you can place your GW1100 there.

Sorry the routers in the Garage and I don’t get a very strong signal in the lounge that’s why I have a wireless extender setup halfway between the garage and lounge . I’ve connected the gw1100 up in the lounge and connected to the wifi extender now . It’s just the construction of the house which is 420 square metres and the Garage being at the far end , just want to have a play with it now as I use to have a 1 wire weather station connected to weather display etc … the author lives locally and I’ve known him for 30 years

you mean you cannot find the SSID of your wireless network in the GW2000 ?
When you put your GW2000 close(r) to your WLAN access point (your wireless router) until you can connect the the wireless network, can it still receive the sensor data ?
If so, place it close(r) to the WLAN router.