BT Home Hub 5 A Nanddump Size and USB location

I have a BT Hub 5 A and have a Nanddump of the BT firmware which is the right size.
I flashed OpenWRT and am now on 19.07.3, I have taken a Nanddump of this running system and am curious that it is smaller. It's only 126Mb (132,644,864 or 131072 x 1012) compared to the BT version which is 131072 x 1020)
I wanted to try a restore to test a modded version, but want an easy route back.
Is this size difference a problem?
Secondly, the nanddump needed to point at /dev/mdt3/ not 4 - any problem?
Thirdly, the USB doesn't auto mount, and took some effort to get working. It's now mounted on /mnt/sda1/. Should I change this to /tmp/mounts?
Thanks
Richard

I'll tackle this one first...

This is fairly easy to setup in the Mount Points menu in LuCI, once the correct drivers, etc. are installed. It likely would be at /mnt/sda1/. Can you explain why you suggest /tmp/mounts ?

The location doesn't exist; and I can't find it in any documentation.

I'm lost at why the size difference would be a problem. You noted the reason this is the case:

They're different "versions" (though I'm not sure I'd use that term, I'd say "made by different people").

Then why don't you susupgrade it?

(Otherwise, it seems like you're trying to alter the binary file and re-flash it. Is that the case?)

Thanks for the quick reply,

I am trying to use the modded version from https://github.com/aszeszo/BTHH5a-fw-mod. His script generates a .Izma compressed file and I didn't know if you could use sysupgrade, so was just following the process.

As for the mount location, I used the guide from here https://github.com/mkresin/BTHH5a-installimage/releases, which does mention tmp/mounts.

Thanks

I think you should ask them, given it's not OpenWrt.