Currently, there is a maximum campaign map speed, which CA has implemented for good reasons.
However, in your great wisdom and foresight you have forgotten to add a minimum Campaign Map speed as far as I can tell. There are too many speed debuffs in Warhamme 2 including the terrain itself which can reduce an armies speed below 50% of normal. I have had Waaagh! armies that were moving near or less than 10% movement speed in swampy areas. Even underground movement can be really slow, which I am not sure how that happens. This is not fun.
50% is the minimum movement speed for a force regardless of terrain for a player to still have fun while still feeling the impacts of campaign movement modifiers. CA please add a minimum campaign map speed to help players deal with all the campaign speed debuffs and/or lack of faction buffs in this crazy game.
Also, consider adding swamp movement (ignore swamp movement debuff) and river movement campaign buffs. Seems like a cool thing players would want for the correct commanders&heroes or after defeating the correct commander.