Poor FTP testing?

I received this email from an athlete with a common question about what to do if you just don't tend to be a good at testing for FTP, with results that seem to match what your race performances show.

Happy New Year Sir,

I've recently gotten through Triathlon 2.0 and Run with Power and have found them to be quite helpful. I was familiar with most of the concepts in 2.0 but you provided a lot of additional context that I was missing before. 

The question, or problem that I have really, is an inability to FTP test well. Over the past few seasons my FTP hasn't risen above 228 (averaged 240 in 20 minute test) but my overall fitness and endurance has steadily improved. Is there a way you would recommend "backing into" threshold power based on a long ride, etc? I'm getting more fit, just not any faster. Comparable 40 mile rides from 2015 and 2016 are done at the same speed, avg power, etc, but my avg HR is 18 bpm less.

I raced Ironman Mont Tremblant in August and while only my second fastest Ironman, it was by far my most complete and well executed race. I knew my FTP wasn't right so I rode race day by feel with an occasional glance at HR. Based on an FTP of 228 my NP was 174, IF was .76, Pw:HR was -0.84% and TSS was 350.2. That amount of stress should have ended my day but I followed that up with my best and first sub 4-hour Ironman run. Clearly my feel for the bike was spot on, but the numbers are not. Is there any way I can derive a more accurate FTP?  

I've recently FTP'd again to assess where I am as I prepare for IM 70.3 Puerto Rico and my test numbers were even worse (avg 217 watts for 20 min) but my average power / heart rate is close IMMT values when I do 1.5-2 hour moderate effort rides.

My apologies for such a long email and I sincerely appreciate your time if you've made it this far.

Thank you,

Steve

My response to Steve:

Steve,

Thanks for the email. You're not the only person who has struggles testing, as that intensity is definitely a bit higher. I tend to find the older the athlete, or the longer they have been doing longer, aerobic training, the harder it is to test well. 

I think part of it also can be how well an athlete responds to a taper. You might be responding very well to a taper, which raises your FTP more than you realize. Also, you need to make sure you are using the same protocol to test, especially in the days before the test, so the results are reliable and the test is repeatable. So if you take a day off in the 2-3 days before the test one time, you need to do that each time. If you don't do this, then you're not comparing apples to apples, as the fatigue you carry into a test can affect the result. 

In general, you are on the right track, using your perceived exertion to better handle the raceday intensity, especially if you feel comfortable with your sense of the intensity, so you can better maximize your performance. 

Hope this helps!

Coach Vance