This is typical for these low cost products. They normally have a low cost/lower power wi-fi chipset to assure they can pass FCC and CE testing requirements on device radiation - we deal with this in a few products our company manufactures, if not you have to spend more to insulate the board and chipset better or go to a different and more expensive antenna. If anyone gets a device like this and must have wi-fi I always say just pickup a linksys or netgear USB plug in which will give you the wifi coverage most desire. As in your case - I always recomend hard wired anyways.I bought this box for streaming 8 cams. Works great with Tiny cam Pro. Wifi sucks, but it has 1Gb lan.
http://www.gearbest.com/tv-box-mini-pc/pp_282312.html
For streaming it was $50.00?I have FIre TV and side loaded Tinycam pro, works great plus it has great KODI on it already for streaming it was $50.00