Thank you Dick. I can now admit I too was shown to start the 2nd Eng with the 1st at IDLE, but have been re-reading the RFM which says to have the 1st ENG at FLT before starting the 2nd.
I'm guessing the reason is for a softer Engagement with the 1st ENG at FLT like the Bell 412 requirement to be at 77 to 85% NR for the 2nd Eng start. Which is where I think the 100 amp recommendation has come from. Even though the 412 RFM says below 150 amps. Most guys I've flown with, wait until below 100 amps.
I haven't been able to find anything in the A109E RFM about waiting for below 100amps, but do have a check of the amps, as that too was shown to me during my endorsement.