Well, since we're dealing with plants and not weighed extracts, it's always kind-of a dice roll on strength of any given plant. The only way to know if you have a potent cutting is to eat it, and note the results. If it's strong, you pup/clone/graft the shit out of the base, and duplicate it.
That said, 1 foot of Bridgesii is usually strong, but Pach is wildly variable.
Personally I definitely wouldn't have strung out the administration over 90 minutes for that light of a dose-- that most surely contributed to the weakness of the trip. Also, I would wonder how effective the 3.5 hour boil was, but as others have said, it might have been just fine-- there's really no way to know because that plant is gone.
It takes awhile to metabolize the alks anyway, but if you figure nearly an hour to begin hitting your system, the three would have overlapped with the complete amount for a shorter time-- this caution would make sense if you were dosing a known strong cutting, but as a foot of Pach is generally pretty modest, even for regular bridge I'd have taken it all at one sitting as mentioned above.
It's always a challenge to know what you're in for until you've tried it-- erring on the side of caution is never bad, but it can result in weak experiences-- as you have found. You could try this with a Bridge cutting (or an unusually strong pach) and find that 8" would have layed you out in cosmic-ass-kicking territory for 13 hours. Don't be sorry, hehe-- it's a part of the experience to have weak plants involved.
I have a 16" hybrid Pach/Peru and a ~1 foot cutting of a etiolated bridge that I combined together over the weekend-- it's in my fridge now, reduced to about 200ml (half pint or so) of thick brown syrup. I boiled it with a touch of vinegar for 24 hours continuously.
I'll use my listed prep method with it, and will take it all within 30 minutes.
I am confident in doing this because I have used 3 identical cuttings of the same hybrid before, and found that 2 segments was strong, one was mild, therefore the 16" hybrid + the foot of 1.5" etiolated bridge tip will get me somewhere between the other two experiences.