Item Group Wise Discount Percentage

Hi Team,

I am trying pricing rule to achieve quantity based discount % scenario in sales order as i am unable to fix it using pricing rule.

Use case:-
In a sales order if i take different items belongs to a same item group and if the sum of the quantity lies between 1-4 the discount_percentage should be 70%
and if the the sum of the quantity of the same group goes more than 4 i.e 5-9 it will be 78%,

Please suggest me some solutions, i tried with pricing rule and its not working as per requirement.

Thanks in advance,