I have a now retired P2V whose video range was only anything between 500' and 800' more often than not dropping out on the lower end of that range (one reason why I retired it), despite the range being quoted as 300m. Quoted ranges, then, are not to be trusted since such ranges can only be achieved in perfect conditions, though it is true to say that some people achieve better ranges especially if using antenna boosters.
Since the P2V, UAS' have come a long way and video ranges have also increased. For example, my P2V+ can give a video range all the way out to my maximum VLOS (1200' as a dot in the distance). Same with my H480 (1500' that I can vouch for). 1200' feet, then, is reasonable for a T4K...Far better that earlier UAS'.