Nice post ranging1 you hinted to what i was going to say. If taller people do not necessarily have more test than shorter people it makes sense that in comparison to their height tall people find it hard to look as big. While both of their bodies may allow them to gain 20lbs during a cycle, the 20lbs will look alot more on the 5'9'' guy than the 6'3 guy! so maybe if your taller you still only have 'x' amount of testosterone so can only sustain 'x' amount of lean body mass.
this makes sense why shorter people seem to look like they bulk up quicker when natural, they have more test naturally in comparison to their height so it appears as tho they are bigger. i have a mate who is 6'6 and has put on 6kgs ive put on 3 and i look like ive put on more muscle than him just cause his muscle bellys are alot longer.
Height weight and body composition all come into effect.
Got to remember tho not everyone has the same amount of test naturally in your system anyway, a shorter guy might have more than a taller guy its all genetics.( as it always is in this game

, i say that with a sad face cause my genetics suck !! )