I play similarly and can get stealth down to the same range, sometimes lower at night. T6 Assassin gear with stealth-friendly mods. Rogue armor I think would go a couple of points lower on the stealth meter but I want the Assassin benefits for zombie forgetfullness.
Amongst normal sleepers, those single digit stealth values do really well, specially if you can keep to a distant proximity.
Where stealth is challenged is in our expectations compared to the POI creator's expectations when there are triggers and/or minscripts. Because triggered zombies aren't placed until triggered, the only proactive element available to the stealth player is battlefield modification which can enable an escape and the reacquisition of stealth.
The interests of the POI creator, perhaps wanting to tell a story where zombies have wandered into a previously cleared area, conflict with player expectations and effort that they have cleared a safe space. A POI creator who wants to show a series of zombies crawling out of an air duct needs the minscript and waves while the stealth player has to keep running off and reacquiring stealth.
Some players reject the notion that fleeing and reacquiring stealth is desirable game play. I, personally, don't mind that technique except for POIs where that seems to be most of the encounters.
Group play and stealth is pretty awkward, though I recently played with a group where the three regular players took stealth and that was working - right up until two other non-stealth players showed up and joined.
I have been wondering if the triggers and minscripts might be getting overused. Or, if not, then perhaps there might be some "randomness" to the reaction of zombies that have been triggered such that maybe some are wanderers unaware of the player, or something else.
While the game is probably working at intended, not all stealth players probably agree. I largely agree the stealth system is probably working fine, but the POI composition is probably working against perceptions and I don't know if the use of triggers and minscripts will moderate, get larger, or what.