I think whatever you end up with, the combiner box should be in an area easy to sure.
From good advice I got here, I changed my original plan of putting the combiner box on the hard to get to roof to the easy to use area next to my batteries. Made trouble shooting and posting the system on and off easy. I need to shut off the solar panels before removing battery power. I would have hated to climb to the roof each time to do it.
In my case I used 10 AWG from panels to the combiner box, and then 6 AWG from the combiner box To the SCC.
I first check ampacity to be sure the wire can handle the amps:
When selecting a cable, one must know its wire ampacity rating. This rating has been determined by the NEC (National Electrical Code)..
www.wireandcabletips.com
So no matter the volatage loss, for 10 AWG wire size I won’t use it more than 30 amps. Ampacity doesn’t care about length. Voltage loss does.
I then go to a website for a DC voltage loss calculator like this and try for less than 3% voltage loss with wire size and length:
This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.
www.calculator.net
Distance matters on voltage loss and will make a big difference.
I use 100 watt panels on two different strings and I use 175 watt panels to another SCC. Not quite 250 watt panels, but I’d do the same thing if I were calculating for 250 watt panels. I also built to be able to add panels on, which for the most part I have. The bigger combiner box I ran out of room for panels and can’t add on though.