I don’t get the problem. If you think that the Harman target for IEMs is not appropriate. Create your own one. This is easily done with EQ. And if you have found it, you can listen to it by EQing any IEM to it, why do you need an IEM for it to have this as a stock tuning?
Could it be that IEM’s don’t have the springy headband and heavy clamp of an HD 650? 
IEM tips don’t compress rapidly like HD 650 pads, whereby the FR doesn’t change as much? 
Seriously, I’m not sure that the HD 650 profile should be the goal. It’s not my ideal sound at all, and I don’t even like its timbre unless run from a tube amp. While popular among some and a strong legacy benchmark, I find its mid bass to be forced and excessive. I find it easier to EQ up frequencies with naturally lean or neutral (headphones) rather than control their excesses – either with the HD 650’s bass or bright treble. IEM EQ – especially BA IEMs – may differ.
@Garrincha has a valid point – Simple EQ solves many issues and customizes products to a person’s specific anatomy and hearing. Separate channel/balance controls also work around left-vs.-right ear anatomy variations and hearing loss differences. This alone can result in a notable perceived staging and quality boost.
Welcome @Garrincha.
I’m not too familiar with IEM tuning at all, but this portion completely addressed one of the biggest issues I’ve personally had with some of my IEMs. One of the first IEMs I got was the Dioko, with most describing it as mostly neutral but with some hotness in the treble.
I knew I was decent on handling treble, but when I got it, I found there to be some ear-piercing frequency that I couldn’t deal with at all. It sounded kinda like sibilance and I assumed the rather suspicious looking 8kHz (yes I am aware of the inaccuracy), but after eq-ing it just to check, found no improvement at all (no surprise there). However, after retuning it with some of the 5128/4620 measurements (in that 10-14kHz), I found it had significantly reduced that issue, putting the IEM back into my comfort levels.
I didn’t see many reviewers talking about a similar problem, so perhaps I am just extra sensitive to that region. Even tried swapped filters (I didn’t get an early batch), which of course made no difference. Honestly, I’m just glad to know I wasn’t crazy for hearing some weird peak, and saved me a lot of time trying even more mods.