My old R18 had bow mounted fuel tank. Think it was factory fit (??) but others may know differently.
No problems with pumping fuel from bow - rigged with 2.4 200 and standard diaphram pump.
Only issue for us was that the fuel tank provided ballast that couldnt be adjusted. Used to stuff quite a bit when tank was full
but was more flighty when tank got empty.
Id guess that by mounting tank in stern you have option to fit a bow ballast tank and adjust according to conditions.
Our R21 has stern mounted tank