Does economy fare class affect points upgrade ability/cost?

If purchasing a domestic economy fare on either Virgin or Qantas, with the intent of using FF points to upgrade to business class, does the economy fare class you book with affect the either
a. weather you can even use points to upgrade
b. the amount of points you need to use to get the upgrade

Basically my strategy on Virgin is for my employer to pay for economy flights on work trips, but I use my FF points to get the upgrades. But If I need to buy are particular class of fare to allow this to happen, what fare do I get them to book?

Hi doctorj,

This pointhacks article might be of use.

Which fare class NOT to book with Qantas & Virgin Australia to upgrade using points