Discounts doubling up

Hi,
I’ve installed your plugin as I need to create a quantity discount for all products in two categories. Basically, all items are £3.65 of 3 for £10 and £7 or 2 for £10 in the other.
I’ve created rules based on both cart quantity for one category and quantity discount in another. These are based on giving a fixed discount per quantity step (i.e 3 for 10 is £0.95 cart discount, 6 for 20 is £1.90 cart discount and so on).
The first rule works fine but it then doubles up on the second rule.
I’ve tried setting different priorities but nothing seems to be working.
From this image – https://postimg.cc/5YRKMf6z – from the quantity, it should be a discount of £8 for 4 units but it’s also adding the original discount of £4 for 2 units as well.
Any advice would be appreciated.