I'm playing an Undead warrior. I sent out 5110 off specs to a target with the "has been attacked a Couple times" stage of GBP. The target was 106.8% of my NW. Their kingdom was 88.6% the NW of mine. My hit (traditional march, no time modifier) was for 9.1% of my acres. We do not have any relations currently.
The issue is that I only received 128 promotions - a conversion rate of only 2.5%!
I believe UD conversions are linked to gains, from my experience.
My gains modifiers from science: +5.5% Battle Gains
I did have anon up, which if I understand correctly, gives -15% gains.

Even with anon and slight GBP, I'd expect more than 2.5% converts - between killed units and promotes, I only gained 61 elites!

My personal Support ID is D5E160D4.