So, what is the point of an incremental contract or do players not on an incremental get a lower match fee?
After a little background reading - it looks like it's all to do with who pays the player rather than what the payer is paid. Whether this still applies to those without any sort of contract I don't know.
"For players holding a 12-month Central Contract, an England retainer replaces their County salary, with the County retaining the player’s registration. If the player is made available to his County, this will be on a free-of-charge basis.
The ECB may offer additional 12-month contracts, known as Increment Contracts. Likely recipients include those players who would be expected to feature regularly in the England ODI and/or T20 teams, but who are not well-established in the Test team. With England Increment Contracts, the County continues to pay the player’s salary, with ECB paying the player an incremental salary. The County receives compensation from the ECB for matches missed while on England duty."
http://www.thepca.co.uk/england_contracts.html