Man, you are missing the time parameter in my opinion. And of course not, half life doesn't change because of dosage. Still the effect of 0,5 mg will drop faster than 1mg because of that very short half life of 6 hours. And if 0,5 mg has about the same effect of 1mg in the first hour, it does not on a 24 hours period. That 's simple, After 24 hours (4 life times) you ve got about 0,125mg of fina in your bood. And a dose of 0,1 mg in your blood reduces DHT by 10,8% which is weak. If you talk 0,5 every day, you ll do fine on the first 12 hours of your cycle. Then after 12 hours, you ll have the equivalent of 0,5/4 mg which means 0,125 mg which reduces DHT by 53%. And right before you take your 2nd pill you ll be somewhere close to one 16th of the 0,5 mg dose you took which reduces DHT by an amount close to 11%.
So on each last 12 hours period of your daily cycle, your DHT reduction will decrease from 53% to 11% within 12 hours. Which is absolute bullshit to stop hairloss.
If you want to take less fina and have the same effect, you can go 0,25mg the Morning and 0,25 mg in the evening, that 's about the same effect as 1 mg daily with half the dose.
This is why people have to use finasteride daily, and they are not forced to do that with dustasteride, since its half life time is 170 hours which is much longer than 6.
I think your account is not right, let me explain. From what I understand, you simply take the 0.5mg and take 2 half-lifes of 6 hours, which will mean that around 0.5/2 = 0.25/2 = 0.125 and then simply multiply it by 10.8% and you arrive at around 11% at 12 hours. I think the data you present is rather too simplified to give a genuine account of what happens in the human system.
The first question that comes to mind is: is the efficacy of a medicine so strictly correlated to the levels of medicine in the human body. So, does it truly mean that if you take 0.5mg of finasteride, the efficacy is cut in half after 6 hours? It's really not that obvious, because a lot of medication actually produces effects that last for days, maybe weeks, even though the half-life is fairly short. So, you can take finasteride, for instance, have it all out of your system by noon, but still suppress DHT because the effects of finasteride have not worn off.
This seems true to a certain extent, because DHT levels return, upon discontinuation, to normal levels after 14 days (1). Furthermore another study found that "Serum DHT levels were studied initially and after 4 months. A daily dose of finasteride 1mg (Group II) induced a 12-54% DHT suppression (avg. 41%) after 4 months. Finasteride 1mg once every 3 days (Group I) achieved a 7-46% suppression of DHT levels (avg. 21%)". (2) This is important, because after 3 days the DHT levels are still suppressed. Meaning that the simple multiplication you proposed is incorrect, since at the beginning of day 3 DHT levels are lowered whilst finasteride is probably out of their systems or very low. Your statement seems therefore incorrect.
Again, the findings are still solid:
"RESULTS:
Scalp skin DHT levels declined significantly by 13.0% with placebo and by 14.9%, 61.6%, 56. 5%, 64.1%, and 69.4% with 0.01, 0.05, 0.2, 1, and 5 mg doses of finasteride, respectively. Serum DHT levels declined significantly (P <.001) by 49.5%, 68.6%, 71.4%, and 72.2% in the 0.05, 0.2, 1, and 5 mg finasteride treatment groups, respectively." (3)
Meaning that 0.5mg finasteride is very close to one and five mg finasteride. Never in the paper is it discussed that a higher dose should be used because of the half-life etc. Therefore their conclusion was: "Doses of finasteride as low as 0.2 mg per day maximally decreased both scalp skin and serum DHT levels. These data support the rationale used to conduct clinical trials in men with male pattern hair loss at doses of finasteride between 0.2 and 5 mg."
The 1mg could as well have been 0.2 or 0.5 or 2mg for that matter, as long as it was higher than 0.2. Therefore, there is good rational to deviate from the 1mg and use 0.5mg if you want to, for instance, safe money or (speculatively) lower adverse effects.
There are little studies that studied a dosage of less than 1mg of finasteride. But I don't see a reason why 0.5mg finasteride each day is that much worse than 1mg finasteride each day.
1)
https://www.ncbi.nlm.nih.gov/books/NBK513329/
2)
http://martinelangsam.com/wp-conten...l-Medicine-Article-published-in-Forum-USA.pdf
3)
https://www.ncbi.nlm.nih.gov/pubmed/10495374