The kits are formulated for a 5 gallon postboil.
IE: If you normally collected 6 gallons @ 1.034 (ish) and boiled for an hour, lost a gallon to boil and chilling you would end up with 5 gallons of wort with an OSG of 1.044 if you got around 70% efficiency. Now this would also theorize that you had no trub whatsoever which is not possible so you would then drain 4 (ish) gallons to the fermentor as you will lose around .5-1.5 gallon depending on your exact setup.
With your parameters* you should have seen this:
*( assuming 70% effic, 2 gallon boiloff, 7.25g preboil collection.)
A. Preboil OSG @ 7.25G : 1.030
B. Boiloff of 30% per hour = 2 gallons boiled off in 1 hour
C: If you truly had 5G left in the kettle it should read around 1.040
Being that you are stating you read an OSG of 1.034 thier is something fishy with your measurement/s and I am leaning towards your boiloff rate first before other factors. It is true larger kettles will genrate more of a boiloff rate but 30% is awful high I am going to lean on 21% overall including chilling. This would leave you with 5.75 g wort @ 1.038.
Or your not accounting for trub loss and had a “normal boiloff” rate of overall 17% which would see the 7.25G reduced to 6 G after boiloff and chilling. You then racked only 5 G as the other gallon was locked up in trub/ other etc… This would spell out a perfect 1.035 to match what you saw.
Just throwing out the possibilities per what math we have to work with. Downline try to accurately gauge what your boiloff rate is, preboil collected, postboil( before chilling), postboil (after chilling), amount collected in fermentor, amount left in kettle>>>this is the total volume of wort, trub, hop particulates left in kettle. Then you can gauge what your true preboil should be to receive 5.25G finished wort in fermentor.
IE: I get 5.25G in the fermentor, BUT I have to assume a 6.3G post boil/chill etc…and make my recipes based off of 6.3 instead of 5 G and expect to lose 1 G to trub etc… So All my recipes if based off kits have to be boosted with base grain to get the OSG to agree with what was meant for a 5G postboil. Yah dig?
Here is an example:
NB Helles = 9# pils malt / .5# Carapils = 1.049
(Assuming 70% Effic / 5 G post / Unknown NB preboil for formulation batches / Unknown loss)
My Helles based on same recipe = 10.5# pils / .5# Carapils = 1.049
(79% Effic / 7.5G preboil / 6.3G postboil / 1G loss / 5.25G to fermentor.)