New Site Conversion Ratios And Sponsor Growth

So i was wondering, do you folks see a correlation between the growth of a new affiliate program and their conversion ratios for the sites in the program?

I know for me that typically, when a new program launches who has sites that i like the look of, the first 3 months of that programs lifespan is when the programs sites sell the best for us.

Then slowly, as the sites become older, conversion ratios start to drop.

Does anyone else notice this and, if so, how do you handle it, is there anything that we can do as affiliates to maintain conversion ratios at the same level as when a program first launches or is it all totally out of our control?

Regards,

Lee