NCBusa,
Ive had two experiences where I was pulled over and asked that same question(if its harder to get motorcycles on radar)....I got two different answers....First, one cop pulled me over and told me he couldn't "lock in" on me because I went by him to fast, but he knew I was well over the limit so he pulled me over and gave a warning, he said that he was using a ka band radar and that on some occasions he will have trouble reading a speed from a motorcycle, but he also added most of the time he'll get them.(nice cop by the way)
The second time a cop got me by lazer, and he told me he read my original speed from my helmet as I crested over the top of a hill (If he wasn't bullsh-ting me, laser must be pretty dam accurate) This one cost me some cash! anyhow, it seems to make a big diffrence on how good and what type radar equipment each individual cop has.