Heart rate adaptation to training and impact on training effort

Hi All, this is an open question hoping you can help explore and understanding this topic more.
I’ve been training for 5 days a week regularly for almost a year now. I raised my FTP three times and I’m at week #5 of criterium medium volume now. Here’s what’s happening:
I noticed that my heart rate is now going up anymore to Zone 5 as I got used to the effort very well. This is reflected by the EPOC in the Garmin staying low and my Garmin training load going down. This comes with a stable Vo2max at my highest ever for a few weeks. A the end of training I don’t feel exhausted and breathless like I used in the past.
At the same time, I tried to do a ramp test and see if the FTP increased but It’s not the case, I tried a couple of times last month but in both cases, it did not raise.
I thought what I experience could be due to increased power, but now I’m confused about what steps to take next to make sure I get full advantage of my training.