hmmm, well maybe some peeps that have experimented with various grates can chime in with specifics, but i'm not sure the grate will solve your problem. (I could be wrong, I'm about 170 lbs soaking wet)
I rode a 96 xp for 3 yrs, beat the crap out of it, the nose always tended to come out of the water a little bit when sitting back in the seat. I probably spent half my time on the ski standing up to be honest, kept the nose down and allowed my knees to absorb the bumps.