AeroPod, PowerPod and Newton

Hi. For less variability and more consistency in testing for power improvements throughout training, I thought it would be better to do the fit test indoors. Is there anything about the fit test that's inappropriate to do on an indoor trainer? I just did 2 chris Carmichael style 8 min field trial efforts to establish comparisons and will post those for those users who are interested in using his systems. I've read that multiplying the avg power by 90% is a good FTP approximation. It's not easy to get 8 minutes without cars whizzing by and lights in Miami (let alone 20 minutes!) I figured the rigidity of the trainer makes test simulation much more accurate and any changes could only be due to rider fitness . Rider mood, time of day etc. are also interesting variatins but you have to draw the line somewhere!
Thanks