The fleet is a nerf
12+d6 is higher on average than 6+rerollable2d6
It's also a relative nerf. The average threat range of fleet units went down while their maximum remained the same. For non fleet units, their average range increased slightly while their maximum range increased massively.
12 +d6 = 15.5 average.
6 +2d6 reroll one or both:
6 + 4.75x2
6 + 9.5 = 15.5 average.
If charging 9- 13 inches or less, you are now less likely to make your mark than the 100% chance you had before. However, you'll only go 8 inches 1/1296 times. a statistical non factor.
10 inches will happen 1/648.
11 inches 1/324.
12 inches 1/167
13 inches 1/83.5
31 in 1296 times, you will fail to go 13 inches.
or in more comprehensible numbers, about 1/41 times.
this part is a nerf.
HOWEVER!!! it's a little one. roll double ones on twin linked, and that's about your odds.
now for the real meat of it. lets look at that magical 15.5 number that is the average for both charge distances.
the old way: you will achieve that distance 1/2 of the time.
the new way: you will achieve it 3/4 times.
Don't try to make a 17" charge. ever. Other than that, you should be fine.