I looked at the spec.
They have a recommended ground plane length of 60 mm, and test data taken on a 90 mm ground plane with a cable attached. Seems a bit odd. Like cheating? weird. I'm sure there is a reason though. Maybe to sell more. VSWR looks best with 60 mm groundplane and Patterns look best with a larger ground plane???
The ground plane length is often a tuning element, so it can be critical.
I'd ask the manufacturer why the recommended and the tested ground plane sizes are so much different. If you're using this as a handheld device, you may want to add some rubber edge protectors to the two long sides to keep your hand off the ground plane. It'll help with range.
good luck,
Kevin