Ah, wargaming scales...
Much of the confusion stems from exactly where you measure to. Some choose to measure "foot to eye" and others "foot to top of head". Both methods have their merits but it sucks when it's not made clear which is being used. Then there's the question of "how tall are these guys in the real?" which often leads to slightly silly discussions, because most model lines don't actually have short guys in them to skew the average.
Assuming 28mm in BF:Evo is to the top of the head, 1:65 is actually on the small side already - 1:60 would be better. If it's 28mm to eye level (making the model something like 30-32mm to the top of the head), then the scale should be more like 1:55. Goes to show what difference a few mm makes! And then we're not even talking about the 3-4mm or so from the base...
In general, I've found it's better to have vehicles a bit too large rather than a bit too small, to compensate for the vagaries of base height and perspective. Large vehicles will look bulky and impressive - small vehicles will look like toys.
The math: Take a good near-average Western male height like 1700mm, divide by your figure's height in mm, and you get your 1:XX scale. Like so:
1700/28=60,71 so scale around 1:60
1700/30=56,66 so scale around 1:55
This works in the reverse as well; divide your 1700 by the figure's scale and you get the height in mm of a figure on the table. Using Mongoose's 1/65 scale:
1700/65=26,15 so Mongoose vehicles would go really well with 25mm models...