Again - it's a combination of prestige, recruit rating, distance and some unknown random thing. I just finished my D2 recruiting and pulled down a D1 player at 150 miles with 10 ST + offer. Another pulldown took 16 STs at 250 miles: 10 ST followed by an "I'm not sure" email, followed by 6 more ST.
Many moons ago I had to send 25 STs to get a player to drop, but he was an exception.
I've noticed that ratings are kind of an unpredictable gauge. I've had players who were well within my target range who flat-out told me not to call them ever again, while another player with a higher rating will commit for a minimum of effort.