Hi, if you look at your chances of finding a suitable field from an agricultural standpoint, you will realise that it is the time of year which is a major factor in finding a good field....
Nov, Dec, Jan, Feb, most fields will be waterlogged, unless frozen.
March, Apr, May; Firm ground and short crops in almost every field.
June, July, Aug; Lots of growth = tall crops. Only harvested grass fields or grazed pasture land available ('Hey you, watch my cows!')
Sept, Oct; Most fields now harvested, but some now ploughed up again.
If size really matters, some counties have some very small, stone walled fields (Yorkshire, Scotland etc.) Whereas Linolnshire and that flat Southern area has some very large 60+ acre flat fields.