Example:

Product A is cost priced at $100, and given a mark up of 30%. 

Product A has a template price added at $80.00. (the max discount is 100%)

The maximum discount that is available to this product should be 23%.  (anymore and the surgery will lose money)

I apply a TYPE discount to the product that can give up to 28%

Customer A is charged for the product they have no discount type so they pay $210.00 (130 +80)

Customer B has Disc28 (28% type applied) currently they are charged. $151.20 and recieve a discount of

$58.80 or 28%. 

This is incorrect they should only recieve the maximum discount. The maximum discount would have been:

(130 x .23) + (80 x 0.28)

$52.30

I would advise that the maximum discount be defaulted at the product margin at price creation.  The administrators can set it to be up to 100% manually.  Please note margin and markup are different. Margin = 1/(1+(markup%/100))