Many vendors use percentage pricing for support. For instance, basic support may be priced at 18% of the license price. Would it be wrong to use a fixed price instead?
Fixed prices are just fine. They are very simple to communicate and they can have an effective dampening effect on discount requests. They can be easier to manipulate on price lists and quotation forms.
On the other hand, fixed prices can be awkward when you need to scale them for customers with more licenses or more products. If all your customers use the same product, no problem: charge them all the same amount. But it makes little sense to charge customers the same amount for 1000 licenses or 1 — nor can you charge the customer with 1000 licenses 1000 times more than the customer with the one license.
So before you fall in love with fixed pricing be sure to check how it will scale for larger customers. You don’t want to either leave money on the table or be seen to be gauging your largest and typically most important customers.