I think generally yes, phenethylamines are the primary compounds known to work in the same dose range as LSD. Unfortunately they are much cheaper to produce, and the majority of the 25C- and 25I-NBOMe fatalities occur after people believed they were taking LSD. I have read similarly, that tab size of a dose might be an indicator, but I don't think it's a fully reliable method. Check out the old 2013 Erowid "Spotlight on NBOMes" article [1]-
> Silk Road prices for pure 25I-, 25C-, and 25B-NBOMe powder currently range from $90 to $200 per gram. The most problematic listings are vendors selling blotter that begs to be resold as acid: 1/4-inch perforated squares in 100-hit sheets bearing designs such as Albert Hofmann's bike ride and The Beatles Yellow Submarine, among other acid-blotter designs from the past. One vendor states "each tab is acid size, no big blotters here". Another offers hits supposedly containing 1 mg of 25I- and 25B-NBOMe each! Dosages range from 500 micrograms to 2 mg per 1/4-inch hit, with advertised doses averaging around 1 mg. On Silk Road, LSD blotter is 5-10 times more expensive than NBOMe blotter.
I think unfortunately toxic and potentially fatal doses can fit on a 1/4 inch hit or in a single liquid drop. There needs to be a lot more active chemical though, whereas you get a slight metallic taste with LSD, the article says NBOME is extremely bitter due to the higher concentration, which is sometimes covered up with mint or other flavor (never heard of this with LSD).
There's an interesting 2019 article "Multimodal imaging of hallucinogens 25C- and 25I-NBOMe on blotter papers" [2] that analyzed a random seized NBOME sample from Germany. It has lower concentration per cm² than what Erowid cited, but I don't think it's a technical limit unfortunately that prevents scary doses from fitting on a standard blotter.
[1] https://erowid.org/chemicals/nbome/nbome_article1.shtml
[2] https://analyticalsciencejournals.onlinelibrary.wiley.com/do...