Canvas roof bags

Hi guys

Maybe a silly question, but then again ...

I'm looking at getting a canvas roof rack bag for the cruiser. Looking on the Southern Cross & MSA websites, their bags are both 1200mm wide.

Our ARB roofrack is 1120mm wide, meaning these bags are too wide. Is the 80mm extra width of the bag likely to create any issues/problems?

The alternative is to have a bag made up, but I'm assuming that 'made to order' will cost more than 'off the shelf'.

If you have one of the newer Southern Cross bags, what are your thoughts of them being extendable height wise (25mm to 45mm)?

Also looking at In Front Camping who have a range of different sizes. I like how the flap over the zip goes all the way to the bottom of the bag, but am confused with their comments that the zip (only one zip puller?) runs along one 'long and two short sides' (meaning it opens to the side? and has a covered zip end across the front of the bag - allowing moisture to wick in while driving?). Also what is the quality of these bags like compared to Southern Cross or the MSA bags?

many thanks in advance.
Ian