Oh a good tip too is upping your special mix to suit what you're gonna lift to. Heres an example...
Say we have a client who's a natural level 4 and they want to be an 8, now we know that regular KP can lift up to 3 levels, so we need to switch to a special blonde. That should get it to a 7-8, BUT special blonde shades are designed to neutralise the pigment load on a level 10 which doesn't have as dense a pigment as a level 7-8. So what we can do is add special mix to compensate for that.
So from a 4 you'll see red and orange, you probably wont even see the undertone of a level 8 because theres so much pheomelanin left behind.
But because you're doubling the developer everything gets diluted so we need to also double our pigment load to compensate for that!
So i would use 12/81...
Then according to the rule of 11 which tells us how much special mix to add depending on depth (subtract the depth from 11 and you'll get how many centimetres of special mix you need to add per 30g of kp) i need to add 3cm on a depth 8 but I'm doubling it so i need to add 6cm, id probably use 0/81 and a dot of 0/28 for the red we dont need much of that cause i find its pretty strong then the 8 in the /28 will help again with all the orange.
So our formula is 30g 12/81 + 6cm (3g) 0/81 and a dot of 0/28.
Hope that made sense and helps😂 sorry if ive really confused anyone.