In trying to find the origins of the "Sir Ellis Hicks" legend, I found this 1909 Hicks genealogy. The first chapter is all about Ellis, and is more flowery than a southern California flower farm.
https://archive.org/stream/cotswoldfamilyhi00hick#page/4/mode/2up
The author does, on the page above, make reference to an 1811 work by Playfair with the long illustrious title that starts with British Family Antiquity... citing vol 6, p 121. Finally found this on familysearch:
https://dcms.lds.org/delivery/DeliveryManagerServlet?dps_pid=IE8154299
And in fact, Playfair says this about Ellis on p 121 when discussing the Hicks of Gloucestershire; this might be the earliest reference to the man (unless we can find something earlier); it goes on to describe Robert, father of Sir Baptist Hicks...)
"This founder was the gallant Sir Ellis Hicks, who was made a night banneret in the reign of King Edward III., and had the three fleurs-de-lis given him for his arms, on account of his bravery, and taking a pair of colours, in the French wars, under Edward the Black Prince." [note: no mention of the Battle of Poitiers.]
"From him lineally descended [but he doesn't say how] John Hicks, of Tortworth,[fn o] in Gloucestershire, Esq. who, dying in the 7th year of King Henry VII., left a son[fn p],
"Robert who was a citizen of London, and raised a very considerable estate by his business. He married Juliana, daughter of Arthur Chapham, of the county of Somerset (Kimber says, daughter of William Arthur, of Clapham, in the county of Surrey), Esq. and had issue three sons, viz. 1. Michael, hereafter noticed; 2. Francis, who died young; and 3. Baptist, who taking to business, and by the interest of his elder brother, having great dealings with the court for rich silks and other commodities imported from abroad, acquired a large fortune, and afterwards obtained great honours. Previous, however, to his attaining these, he built Hicks's Hall, in St. John-street, in London, in 1612; and, about the same period, the market-house, and an hospital, at Campden, in Gloucestershire.... He was knighted (some say created a baronet), by King James I., and, in the 4th year of King Charles I., was created a peer, by the title of Baron Hicks, of Ilmington, in the county of Warwick, and Viscount Campden, of Campden aforesaid. His lordship died in 1629, at the advanced age of 78 years.... [and concludes about Baptist leaving two daughters].
[fn o] This place lies in the hundred of Grumbald's Ash, four miles from Berkeley, and twenty-two from Gloucester.
[fn p] Rudder, in his History of Gloucestershire, mentions a Thomas Hicks, who, inright of his wife, Joan Dorney (the descendant of a very ancient family), was seised of lands in Tortworth, and of a fulling-mill, which passed to John Hicks, his son, who died possessed of them in the 38th year of King Henry VIII., leaving his son, John, three years old. The same (or another) Thomas Hicks is also mentioned by Kimber (in his Baronetage) as party to a fine passed during the reign of King Edward VI., in which he is represented as holding lands at Berkeley, in Gloucestershire, concerning which there was a law-suit, that terminated in Thomas's quitting claim, for himself and his wife, Margaret (daughter of James Atwood), to a certain house and lands there, in consideration of 20l. paid by his brother, Robert. A Thomas Hicks, Esq. is also mentioned as the possessor of a handsome house at Peddington, in Berekley, and a good estate. He died in 1746, and was buried at Peddington, in the church, in which there is a momunment to his memory. By these circumstances it appears, that John Hicks, who died in King Henry VII.'s reign, had two sons; and that Robert (mentioned in the text) was the younger one."