Hi,
CNXTim wrote: I suspect this is to do with Hikashop interacting with Bootstrap, but i cannot find out how to fix.
Yes and more exactly, it is how your bootstrap template works.
HikaShop just use the bootstrap classes and recommendations but after that, you template can override how the display will be.
In your case, the image use 100% of the width when the screen is small.
To change that, you will have to create a CSS override for this specific case and check that your new CSS rules does not have side effect on the rest of your website.
Regards,