Need some help!

Work for a company which submits people's qualifications, these qualifications go to our internal verifier's who sample them to make sure they're up to standard. A record is kept of submissions to the IVs who then calculate a 'risk rating' for each employee. They do it by working out a % as the following table shows:

Submissions Achieved Referred %
S A R %
18 9 9 50
28 19 9 47
38 29 9 31
44 35 9 25
45 36 9 25
55 46 9 19.5
99 90 9 10

The aim is for every employee to be 10% or under - low risk

However as you can see in the above example the member of staff (at the beginning) submitted 18, half were fine and half were not up to standard - 50%. However for this member of staff to get down to the desired 10% they'd have to submit a further 81 qualifications and have none of them referred. That is not realistic.

Wondering if anybody had experience of this and can suggest a better way of representing this risk rating?

Thanks in advance