Hi, I'm thinking about brewing a extract full boil in readiness to moving on to AG brewing. I usually do a partial boil and top up the fermenter with cold water etc. In doing a full boil do I have to reduce the weight of hops I use to get the correct IBU level. According to the brewersfriend recipe calculator if I use the same amount of hops in a full boil as in a partial boil the IBU rating goes up dramatically and to get my target IBU I have to reduce my hop weights, is this right?. Also if I want to end up with a 21 litre batch size would I need to have a starting boil volume of approx 25 litres? I must say I'm a bit stuck on this one and any advice would be greatly appreciated.