To be honest, the info on their packs and what they emailed you I feel is a huge cop out especially when their last revision was almost a decade ago!
You could try Casanovum, I have had the odd test which has been a little weird with how the dye is but they are quite wide and seem to take longer for the dye to clear. They sell them on Amazon. I find One Step (the blue handles) wider tests clear quicker but they too can give what appear to be faint lines, although I have seen a difference between yours and mine when dry, mine weren't as clear dry as yours are so perhaps you may have more luck with those?
You could try the Boots or Superdrug own versions of dipstick but I don't know if they are 10miu or more