AdSense Smart About Ad Types?

[cscgal]

Is AdSense smart about which ad types to use for each ad unit? For example, I have an ad unit that performs really well with Images but not Flash, and vice versa with another one. I know that Google says that they will always try to put the highest performing unit (i.e. only an image if you could make more money off of it than a text ad), but what if text ads have such a higher CTR that images drive down your overall CTR and therefore your CPC and eCPM?

[InsightsDigital]

It supposed to.
Something similar happened with one of my campaigns I was monitoring and that is when you may consider temporarily pausing the low performing group on low peak days (day swhich dont have much CTR) and test it this way and see if it impacted the overall performance.

[cscgal]

I'm talking about AdSense, not AdWords.