4 things:
1) If you look at GR Danny's measurements from his upgrade kit, the top end is rolled down compared to everything else. It's far from a flat frequency response. So you might want to look at his upgrade kit.
https://gr-research.com/product/magnepan-lrs/2) Planar speakers have very different characteristics. Have you owned any before? The top end might sound like there is less if you are used to a speaker that has extra top end (like many single driver boxes which have a spike somewhere in the upper mid range or treble range due to the woofer beaming). I find planars to be the most accurate speakers in the treble region and they sound as though the speaker disappears but all of the treble is still there.
3) Planar speakers definitely need some break in time.
4) Do you have the ability to do a frequency sweep measurement? That will really tell you what's going. Are they too close to a wall and reflections are causing issues?
Just some thoughts on this.