good Image to think about.
1) Increase one, and hold the other the same, and you go faster. Yay!
2) Increase one at the expense of the other and it's an even trade.
3) Decrease both and it's time to call it a day ;-)
OK, (3) expands the area of your envelope. Very good!
Otherwise you will get best area if you "design" your envelope with both sides equal-lengthed...
...Damned not everybody likes squared envelops, and damned
, both sides don't have the same unit of measurement... :-))