Did you do a full 4DP test before starting your plan? Since you started training several months ago I was wondering what your baseline is and when it was set. A 10% or more gain after 17 weeks from ground zero would be quite achievable, but much more of a challenge in 6 weeks if you tested at the start of your 12 week plan. I don’t think the HM test will in any way cap your percentage gain, so just smash it as hard as you can at the time and see how you go!
It is based on the numbers you score and they say you won’t be able to finish all the steps of the ramp test. Let’s say you get to the end, so the maximum would be a percentage (FTP = 75%) of the average power of your last minute.
So there is a limit, but hard to be achieved.
I did one HM at week #8 of my plan and increase my FTP from 218 to 252 W (I’ve failed 3 steps to the end). Then last Sunday I did FF at week 12 and achieved 257 W.
I believe it is not difficult to see a 10-15% increase in your case, but each one responds a different way.
Great to hear you have HM coming up! This will be a great time to re-assess those numbers which will be beneficial for you as you mention you are feeling stronger so it will adjust your FTP and MAP targets for the remainder of your plan. Here is some extra info you can check out also:
When HM was tested last year I tried it and reached the end. At that time they used to say it was impossible to finish all the steps. I did finish, but later I figured out there was a mistake since I stood up to manage to finish the final part.
That demo version I think used to start at a step of about 50% FTP and had only 13.
The current, official version, starts a bit higher and has 15 steps.
Here the images of my recent HM test (The Suf App and Garmin Connect screen captures) and comparing them to my try with the pre-official version of HM (on Feb 2019).
Comparing both tests I am very happy to reach the third last step and I don’t know if I could reach the second last even if I was in a perfect day for testing.