Great numbers. I assume "Trailer bogie" is the weight of the trailer axle(s) in the specified condition, since the totals for all 3 numbers are within 20 lbs in either condition (good job!).
So by adding the trailer, you removed 200 lbs from the front axle. The goal should be to put all of that weight back on the front axle by engaging the WDH, and you move all but 40 lbs.
That ATV looks to weight 630 lbs based on a quick search. That's approx. 315 lbs of additional TW. Doing some quick calculating from your other numbers, it looks like about 20% of your TW is removed from the front axle [200 / (6800 * 15%)]. Apply that to that 315 value, and the 4-wheeler should remove about another 60 lbs from the front axle.
So, the 40 lbs you were short, plus another 60 lbs from the toy, is about another 100 lbs that you'd need to get back to the front axle.
I would add another washer or 2 to get the head tilted down a bit more.
thebrakeman ('70), DW ('71), DD ('99), DD ('01), DD ('05)
2004 Surveyor SV261T (UltraLite Bunkhouse Hybrid)
2006 Mercury Mountaineer V8 AWD Premier
Equal-i-zer WDH (10k), Prodigy Brake Controller